delivered the opinion of the Court.
We granted certiorari to decide whether it violates the Fourth Amendment for the United States Customs Service to require a urinalysis test from employees who seek transfer or promotion to certain positions.
I
A
The United States Customs Service, a bureau of the Department of the Treasury, is the federal agency responsible for processing persons, carriers, cargo, and mail into the United States, collecting revenue from imports, and enforcing customs and related laws. See United States Customs Service, Customs U. S. A., Fiscal Year 1985, p. 4. An important responsibility of the Service is the interdiction and *660seizure of contraband, including illegal drugs. Ibid. In 1987 alone, Customs agents seized drugs with a retail value of nearly $9 billion. See United States Customs Service, Customs U. S. A., Fiscal Year 1987, p. 40. In the routine discharge of their duties, many Customs employees have direct contact with those who traffic in drugs for profit. Drug import operations, often directed by sophisticated criminal syndicates, United States v. Mendenhall, 446 U. S. 544, 561-562 (1980) (Powell, J., concurring), may be effected by violence or its threat. As a necessary response, many Customs operatives carry and use firearms in connection with their official duties. App. 109.
In December 1985, respondent, the Commissioner of Customs, established a Drug Screening Task Force to explore the possibility of implementing a drug-screening program within the Service. Id., at 11. After extensive research and consultation with experts in the field, the task force concluded that “drug screening through urinalysis is technologically reliable, valid and accurate.” Ibid. Citing this conclusion, the Commissioner announced his intention to require drug tests of employees who applied for, or occupied, certain positions within the Service. Id., at 10-11. The Commissioner stated his belief that “Customs is largely drug-free,” but noted also that “unfortunately no segment of society is immune from the threat of illegal drug use.” Id., at 10. Drug interdiction has become the agency’s primary enforcement mission, and the Commissioner stressed that “there is no room in the Customs Service for those who break the laws prohibiting the possession and use of illegal drugs.” Ibid.
In May 1986, the Commissioner announced implementation of the drug-testing program. Drug tests were made a condition of placement or employment for positions that meet one or more of three criteria. The first is direct involvement in drug interdiction or enforcement of related laws, an activity the Commissioner deemed fraught with obvious dangers to the mission of the agency and the lives of Customs *661agents. Id., at 17, 113. The second criterion is a requirement that the incumbent carry firearms, as the Commissioner concluded that “[pjublic safety demands that employees who carry deadly arms and are prepared to make instant life or death decisions be drug free.” Id., at 113. The third criterion is a requirement for the incumbent to handle “classified” material, which the Commissioner determined might fall into the hands of smugglers if accessible to employees who, by reason of their own illegal drug use, are susceptible to bribery or blackmail. Id., at 114.
After an employee qualifies for a position covered by the Customs testing program, the Service advises him by letter that his final selection is contingent upon successful completion of drug screening. An independent contractor contacts the employee to fix the time and place for collecting the sample. On reporting for the test, the employee must produce photographic identification and remove any outer garments, such as a coat or a jacket, and personal belongings. The employee may produce the sample behind a partition, or in the privacy of a bathroom stall if he so chooses. To ensure against adulteration of the specimen, or substitution of a sample from another person, a monitor of the same sex as the employee remains close at hand to listen for the normal sounds of urination. Dye is added to the toilet water to prevent the employee from using the water to adulterate the sample.
Upon receiving the specimen, the monitor inspects it to ensure its proper temperature and color, places a tamper-proof custody seal over the container, and affixes an identification label indicating the date and the individual’s specimen number. The employee signs a chain-of-custody form, which is initialed by the monitor, and the urine sample is placed in a plastic bag, sealed, and submitted to a laboratory.1
*662The laboratory tests the sample for the presence of marijuana, cocaine, opiates, amphetamines, and phencyclidine. Two tests are used. An initial screening test uses the enzyme-multiplied-immunoassay technique (EMIT). Any specimen that is identified as positive on this initial test must then be confirmed using gas chromatography/mass spectrometry (GC/MS). Confirmed positive results are reported to a “Medical Review Officer,” “[a] licensed physician. . . who has knowledge of substance abuse disorders and has appropriate medical training to interpret and evaluate an individual’s positive test result together with his or her medical history and any other relevant biomedical information.” HHS Reg. § 1.2, *66353 Fed. Reg. 11980 (1988); HHS Reg. §2.4(g), 53 Fed. Reg., at 11983. 'After verifying the positive result, the Medical Review Officer transmits it to the agency.
Customs employees.who test positive for drugs and who can offer no satisfactory explanation are subject to dismissal from the Service. Test results may not, however, be turned over to any other agency, including criminal prosecutors, without the employee’s written consent.
B
Petitioners, a union of federal employees and a union official, commenced this suit in the United States District Court for the Eastern District of Louisiana on behalf of current Customs Service employees who seek covered positions. Petitioners alleged that the Custom Service drug-testing program violated, inter alia, the Fourth Amendment. The District Court agreed. 649 F. Supp. 380 (1986). The court acknowledged “the legitimate governmental interest in a drug-free work place and work force,” but concluded that “the drug testing plan constitutes an overly intrusive policy of searches and seizures without probable cause or reasonable suspicion, in violation of legitimate expectations of privacy.” Id., at 387. The court enjoined the drug-testing program, and ordered the Customs Service not to require drug tests of any applicants for covered positions.
A divided panel of the United States Court of Appeals for the Fifth Circuit vacated the injunction. 816 F. 2d 170 (1987). The court agreed with petitioners that the drug-screening program, by requiring an employee to produce a urine sample for chemical testing, effects a search within the meaning of the Fourth Amendment. The court held further that the searches required by the Commissioner’s directive are reasonable under the Fourth Amendment. It first noted that “[t]he Service has attempted to minimize the intrusiveness of the search” by not requiring visual observation of the act of urination and by affording notice to the employee that *664he will be tested. Id., at 177. The court also considered it significant that the program limits discretion in determining which employees are to be tested, ibid., and noted that the tests are an aspect of the employment relationship, id., at 178.
The court further found that the Government has a strong interest in detecting drug use among employees who meet the criteria of the Customs program. It reasoned that drug use by covered employees casts substantial doubt on their ability to discharge their duties honestly and vigorously, undermining public confidence in the integrity of the Service and concomitantly impairing the Service’s efforts to enforce the drug laws. Ibid. Illicit drug users, the court found, are susceptible to bribery and blackmail, may be tempted to divert for their own use portions of any drug shipments they interdict, and may, if required to carry firearms, “endanger the safety of their fellow agents, as well as their own, when their performance is impaired by drug use.” Ibid. “Considering the nature and responsibilities of the jobs for which applicants are being considered at Customs and the limited scope of the search,” the court stated, “the exaction of consent as a condition of assignment to the new job is not unreasonable.” Id., at 179.
The dissenting judge concluded that the Customs program is not an effective method for achieving the Service’s goals. He argued principally that an employee “given a five day notification of a test date need only abstain from drug use to prevent being identified as a user.” Id., at 184. He noted also that persons already employed in sensitive positions are not subject to the test. Ibid. Because he did not believe the Customs program can achieve its purposes, the dissenting judge found it unreasonable under the Fourth Amendment.
We granted certiorari. 485 U. S. 903 (1988). We now affirm so much of the judgment of the Court of Appeals as upheld the testing of employees directly involved in drug interdiction or required to carry firearms. We vacate the *665judgment to the extent it upheld the testing of applicants for positions requiring the incumbent to handle classified materials, and remand for further proceedings. II
hH
In Skinner v. Railway Labor Executives’ Assn., ante, at 616-618, decided today, we held that federal regulations requiring employees of private railroads to produce urine samples for chemical testing implicate the Fourth Amendment, as those tests invade reasonable expectations of privacy. Our earlier cases have settled that the Fourth Amendment protects individuals from unreasonable searches conducted by the Government, even when the Government acts as an employer, O’Connor v. Ortega, 480 U. S. 709, 717 (1987) (plurality opinion); see id., at 731 (Scalia, J., concurring in judgment), and, in view of our holding in Railway Labor Executives that urine tests are searches, it follows that the Customs Service’s drug-testing program must meet the reasonableness requirement of the Fourth Amendment.
While we have often emphasized, and reiterate today, that a search must be supported, as a general matter, by a warrant issued upon probable cause, see, e. g., Griffin v. Wisconsin, 483 U. S. 868, 873 (1987); United States v. Karo, 468 U. S. 705, 717 (1984), our decision in Railway Labor Executives reaffirms the longstanding principle that neither a warrant nor probable cause, nor, indeed, any measure of individualized suspicion, is an indispensable component of reasonableness in every circumstance. Ante, at 618-624. See also New Jersey v. T. L. O., 469 U. S. 325, 342, n. 8 (1985); United States v. Martinez-Fuerte, 428 U. S. 543, 556-661 (1976). As we note in Railway Labor Executives, our cases establish that where a Fourth Amendment intrusion serves special governmental needs, beyond the normal need for law enforcement, it is necessary to balance the individual’s privacy expectations against the Government’s interests to determine whether it is impractical to require a warrant or *666some level of individualized suspicion in the particular context. Ante, at 619-620.
It is clear that the Customs Service’s drug-testing program is not designed to serve the ordinary needs of law enforcement. Test results may not be used in a criminal prosecution of the employee without the employee’s consent. The purposes of the program are to deter drug use among those eligible for promotion to sensitive positions within the Service and to prevent the promotion of drug users to those positions. These substantial interests, no less than the Government’s concern for safe rail transportation at issue in Railway Labor Executives, present a special need that may justify departure from the ordinary warrant and probable-cause requirements.
A
Petitioners do not contend that a warrant is required by the balance of privacy and governmental interests in this context, nor could any such contention withstand scrutiny. We have recognized before that requiring the Government to procure a warrant for every work-related intrusion “would conflict with ‘the common-sense realization that government offices could not function if every employment decision became a constitutional matter.’” O’Connor v. Ortega, supra, at 722, quoting Connick v. Myers, 461 U. S. 138, 143 (1983). See also 480 U. S., at 732 (Scalia, J., concurring in judgment); New Jersey v. T. L. O., supra, at 340 (noting that “[t]he warrant requirement ... is unsuited to the school environment: requiring a teacher to obtain a warrant before searching a child suspected of an infraction of school rules (or of the criminal law) would unduly interfere with the maintenance of the swift and informal disciplinary procedures needed in the schools”). Even if Customs Service employees are more likely to be familiar with the procedures required to obtain a warrant than most other Government workers, requiring a warrant in this context would serve only to divert valuable agency resources from the Service’s primary mis*667sion. The Customs Service has been entrusted with pressing responsibilities, and its mission would be compromised if it were required to seek search warrants in connection with routine, yet sensitive, employment decisions.
Furthermore, a warrant would provide little or nothing in the way of additional protection of personal privacy. A warrant serves primarily to advise the citizen that an intrusion is authorized by law and limited in its permissible scope and to interpose a neutral magistrate between the citizen and the law enforcement officer “engaged in the often competitive enterprise of ferreting out crime.” Johnson v. United States, 333 U. S. 10, 14 (1948). But in the present context, “the circumstances justifying toxicological testing and the permissible limits of such intrusions are defined narrowly and specifically . . . , and doubtless are well known to covered employees.” Ante, at 622. Under the Customs program, every employee who seeks a transfer to a covered position knows that he must take a drug test, and is likewise aware of the procedures the Service must follow in administering the test. A covered employee is simply not subject “to the discretion of the official in the field.” Camara v. Municipal Court of San Francisco, 387 U. S. 523, 532 (1967). The process becomes automatic when the employee elects to apply for, and thereafter pursue, a covered position. Because the Service does not make a discretionary determination to search based on a judgment that certain conditions are present, there are simply “no special facts for a neutral magistrate to evaluate.” South Dakota v. Opperman, 428 U. S. 364, 383 (1976) (Powell, J., concurring).
B
Even where it is reasonable to dispense with the warrant requirement in the particular circumstances, a search ordinarily must be based on probable cause. Ante, at 624. Our cases teach, however, that the probable-cause standard “ ‘is peculiarly related to criminal investigations.’” Colorado v. Bertine, 479 U. S. 367, 371 (1987), quoting South Dakota v. *668Opperman, supra, at 370, n. 5. In particular, the traditional probable-cause standard may be unhelpful in analyzing the reasonableness of routine administrative functions, Colorado v. Bertine, supra, at 371; see also O’Connor v. Ortega, 480 U. S., at 723, especially where the Government seeks to prevent the development of hazardous conditions or to detect violations that rarely generate articulable grounds for searching any particular place or person. Cf. Camara v. Municipal Court of San Francisco, supra, at 535-536 (noting that building code inspections, unlike searches conducted pursuant to a criminal investigation, are designed “to prevent even the unintentional development of conditions which are hazardous to public health and safety”); United States v. Martinez-Fuerte, 428 U. S., at 557 (noting that requiring particularized suspicion before routine stops on major highways near the Mexican border “would be impractical because the flow of traffic tends to be too heavy to allow the particularized study of a given car that would enable it to be identified as a possible carrier of illegal aliens”). Our precedents have settled that, in certain limited circumstances, the Government’s need to discover such latent or hidden conditions, or to prevent their development, is sufficiently compelling to justify the intrusion on privacy entailed by conducting such searches without any measure of individualized suspicion. E. g., ante, at 624. We think the Government’s need to conduct the suspicionless searches required by the Customs program outweighs the privacy interests of employees engaged directly in drug interdiction, and of those who otherwise are required to carry firearms.
The Customs Service is our Nation’s first line of defense against one of the greatest problems affecting the health and welfare of our population. We have adverted before to “the veritable national crisis in law enforcement caused by smuggling of illicit narcotics.” United States v. Montoya de Hernandez, 473 U. S. 531, 538 (1985). See also Florida v. Royer, 460 U. S. 491, 513 (Blackmun, J., dissenting). Our *669cases also reflect the traffickers’ seemingly inexhaustible repertoire of deceptive practices and elaborate schemes for importing narcotics, e. g., United States v. Montoya de Hernandez, supra, at 538-539; United States v. Ramsey, 431 U. S. 606, 608-609 (1977). The record in this case confirms that, through the adroit selection of source locations, smuggling routes, and increasingly elaborate methods of concealment, drug traffickers have managed to bring into this country increasingly large quantities of illegal drugs. App. 111. The record also indicates, and it is well known, that drug smugglers do not hesitate to use violence to protect their lucrative trade and avoid apprehension. Id., at 109.
Many of the Service’s employees are often exposed to this criminal element and to the controlled substances it seeks to smuggle into the country. Ibid. Cf. United States v. Montoya de Hernandez, supra, at 543. The physical safety of these employees may be threatened, and many may be tempted not only by bribes from the traffickers with whom they deal, but also by their own access to vast sources of valuable contraband seized and controlled by the Service. The Commissioner indicated below that “Customs [officers have been shot, stabbed, run over, dragged by automobiles, and assaulted with blunt objects while performing their duties.” App. at 109-110. At least nine officers have died in the line of duty since 1974. He also noted that Customs officers have been the targets of bribery by drug smugglers on numerous occasions, and several have been removed from the Service for accepting bribes and for other integrity violations. Id., at 114. See also United States Customs Service, Customs U. S. A., Fiscal Year 1987, p. 31 (reporting internal investigations that resulted in the arrest of 24 employees and 54 civilians); United States Customs Service, Customs U. S. A., Fiscal Year 1986, p. 32 (reporting that 334 criminal and serious integrity investigations were conducted during the fiscal year, resulting in the arrest of 37 employees and 17 civilians); United States Customs Service, Customs *670U. S. A., Fiscal Year 1985, p. 32 (reporting that 284 criminal and serious integrity investigations were conducted during the 1985 fiscal year, resulting in the arrest of 15 employees and 51 civilians).
It is readily apparent that the Government has a compelling interest in ensuring that front-line interdiction personnel are physically fit, and have unimpeachable integrity and judgment. Indeed, the Government’s interest here is at least as important as its interest in searching travelers entering the country. We have long held that travelers seeking to enter the country may be stopped and required to submit to a routine search without probable cause, or even founded suspicion, “because of national self protection reasonably requiring one entering the country to identify himself as entitled to come in, and his belongings as effects which may be lawfully brought in.” Carroll v. United States, 267 U. S. 132, 154 (1925). See also United States v. Montoya de Hernandez, supra, at 538; United States v. Ramsey, supra, at 617-619. This national interest in self-protection could be irreparably damaged if those charged with safeguarding it were, because of their own drug use, unsympathetic to their mission of interdicting narcotics. A drug user’s indifference to the Service’s basic mission or, even worse, his active complicity with the malefactors, can facilitate importation of sizable drug shipments or block apprehension of dangerous criminals. The public interest demands effective measures to bar drug users from positions directly involving the interdiction of illegal drugs.
The public interest likewise demands effective measures to prevent the promotion of drug users to positions that require the incumbent to carry a firearm, even if the incumbent is not engaged directly in the interdiction of drugs. Customs employees who may use deadly force plainly “discharge duties fraught with such risks of injury to others that even a momentary lapse of attention can have disastrous consequences.” Ante, at 628. We agree with the Government *671that the public should not bear the risk that employees who may suffer from impaired perception and judgment will be promoted to positions where they may need to employ deadly force. Indeed, ensuring against the creation of this dangerous risk will itself further Fourth Amendment values, as the use of deadly force may violate the Fourth Amendment in certain circumstances. See Tennessee v. Garner, 471 U. S. 1, 7-12 (1985).
Against these valid public interests we must weigh the interference with individual liberty that results from requiring these classes of employees to undergo a urine test. The interference with individual privacy that results from the collection of a urine sample for subsequent chemical analysis could be substantial in some circumstances. Ante, at 626. We have recognized, however, that the “operational realities of the workplace” may render entirely reasonable certain work-related intrusions by supervisors and co-workers that might be viewed as unreasonable in other contexts. See O’Connor v. Ortega, 480 U. S., at 717; id., at 732 (Scalia, J., concurring in judgment). While these operational realities will rarely affect an employee’s expectations of privacy with respect to searches of his person, or of personal effects that the employee may bring to the workplace, id., at 716, 725, it is plain that certain forms of public employment may diminish privacy expectations even with respect to such personal searches. Employees of the United States Mint, for example, should expect to be subject to certain routine personal searches when they leave the workplace every day. Similarly, those who join our military or intelligence services may not only be required to give what in other contexts might be viewed as extraordinary assurances of trustworthiness and probity, but also may expect intrusive inquiries into their physical fitness for those special positions. Cf. Snepp v. United States, 444 U. S. 507, 509, n. 3 (1980); Parker v. Levy, 417 U. S. 733, 758 (1974); Committee for GI Rights v. *672Callaway, 171 U. S. App. D. C. 73, 84, 518 F. 2d 466, 477 (1975).
We think Customs employees who are directly involved in the interdiction of illegal drugs or who are required to carry firearms in the line of duty likewise have a diminished expectation of privacy in respect to the intrusions occasioned by a urine test. Unlike most private citizens or government employees in general, employees involved in drug interdiction reasonably should expect effective inquiry into their fitness and probity. Much the same is true of employees who are required to carry firearms. Because successful performance of their duties depends uniquely on their judgment and dexterity, these employees cannot reasonably expect to keep from the Service personal information that bears directly on their fitness. Cf. In re Caruso v. Ward, 72 N. Y. 2d 433, 441, 530 N. E. 2d 850, 854-855 (1988). While reasonable tests designed to elicit this information doubtless infringe some privacy expectations, we do not believe these expectations outweigh the Government’s compelling interests in safety and in the integrity of our borders.2
*673Without disparaging the importance of the governmental interests that support the suspicionless searches of these employees, petitioners nevertheless contend that the Service’s drug-testing program is unreasonable in two particulars. First, petitioners argue that the program is unjustified because it is not based on a belief that testing will reveal any drug use by covered employees. In pressing this argument, petitioners point out that the Service’s testing scheme was not implemented in response to any perceived drug problem among Customs employees, and that the program actually has not led to the discovery of a significant number of drug users. Brief for Petitioners 37, 44; Tr. of Oral Arg. 11-12, 20-21. Counsel for petitioners informed us at oral argument that no more than 5 employees out of 3,600 have tested positive for drugs. Id., at 11. Second, petitioners contend that the Service’s scheme is not a “sufficiently productive mechanism to justify [its] intrusion upon Fourth Amendment interests,” Delaware v. Prouse, 440 U. S. 648, 658-659 (1979), because illegal drug users can avoid detection with ease by temporary abstinence or by surreptitious adulteration of their urine specimens. Brief for Petitioners 46-47. These contentions are unpersuasive.
*674Petitioners’ first contention evinces an unduly narrow view of the context in which the Service’s testing program was implemented. Petitioners do not dispute, nor can there be doubt, that drug abuse is one of the most serious problems confronting our society today. There is little reason to believe that American workplaces are immune from this pervasive social problem, as is amply illustrated by our decision in Railway Labor Executives. See also Masino v. United States, 589 P. 2d 1048, 1050 (Ct. Cl. 1978) (describing marijuana use by two Customs inspectors). Detecting drug impairment on the part of employees can be a difficult task, especially where, as here, it is not feasible to subject employees and their work product to the kind of day-to-day scrutiny that is the norm in more traditional office environments. Indeed, the almost unique mission of the Service gives the Government a compelling interest in ensuring that many of these covered employees do not use drugs even off duty, for such use creates risks of bribery and blackmail against which the Government is entitled to guard. In light of the extraordinary safety and national security hazards that would attend the promotion of drug users to positions that require the carrying of firearms or the interdiction of controlled substances, the Service’s policy of deterring drug users from seeking such promotions cannot be deemed unreasonable.
The mere circumstance that all but a few of the employees tested are entirely innocent of wrongdoing does not impugn the program’s validity. The same is likely to be true of householders who are required to submit to suspicionless housing code inspections, see Camara v. Municipal Court of San Francisco, 387 U. S. 523 (1967), and of motorists who are stopped at the checkpoints we approved in United States v. Martinez-Fuerte, 428 U. S. 543 (1976). The Service’s program is designed to prevent the promotion of drug users to sensitive positions as much as it is designed to detect those employees who use drugs. Where, as here, the possible harm against which the Government seeks to guard is *675substantial, the need to prevent its occurrence furnishes an ample justification for reasonable searches calculated to advance the Government’s goal.3
*676We think petitioners’ second argument — that the Service’s testing program is ineffective because employees may attempt to deceive the test by a brief abstention before the test date, or by adulterating their urine specimens — overstates the case. As the Court of Appeals noted, addicts may be unable to abstain even for a limited period of time, or may be unaware of the “fade-away effect” of certain drugs. 816 F. 2d, at 180. More importantly, the avoidance techniques suggested by petitioners are fraught with uncertainty and risks for those employees who venture to attempt them. A particular employee’s pattern of elimination for a given drug cannot be predicted with perfect accuracy, and, in any event, this information is not likely to be known or available to the employee. Petitioners’ own expert indicated below that the time it takes for particular drugs to become undetectable in urine can vary widely depending on the individual, and may extend for as long as 22 days. App. 66. See also ante, at 631 (noting Court of Appeals’ reliance on certain academic literature that indicates that the testing of urine can discover drug use “ ‘for. . . weeks after the ingestion of the drug’ ”). Thus, contrary to petitioners’ suggestion, no employee reasonably can expect to deceive the test by the simple expedient of abstaining after the test date is assigned. Nor can he expect attempts at adulteration to succeed, in view of the precautions taken by the sample collector to ensure the integrity of the sample. In all the circumstances, we are persuaded that the program bears a close and substantial relation to the Service’s goal of deterring drug users from seeking promotion to sensitive positions.4
*677In sum, we believe the Government has demonstrated that its compelling interests in safeguarding our borders and the public safety outweigh the privacy expectations of employees who seek to be promoted to positions that directly involve the interdiction of illegal drugs or that require the incumbent to carry a firearm. We hold that the testing of these employees is reasonable under the Fourth Amendment.
C
We are unable, on the present record, to assess the reasonableness of the Government’s testing program insofar as it covers employees who are required “to handle classified material.” App. 17. We readily agree that the Government has a compelling interest in protecting truly sensitive information from those who, “under compulsion of circumstances or for other reasons, . . . might compromise [such] information.” Department of Navy v. Egan, 484 U. S. 518, 528 (1988). See also United States v. Robel, 389 U. S. 258, 267 (1967) (“We have recognized that, while the Constitution protects against invasions of individual rights, it does not withdraw from the Government the power to safeguard its vital interests. . . . The Government can deny access to its secrets to those who would use such information to harm the Nation”). We also agree that employees who seek promotions to positions where they would handle sensitive information can be required to submit to a urine test under the Service’s screening program, especially if the positions covered under this category require background investigations, medical examinations, or other intrusions that may be expected to diminish their expectations of privacy in respect of a urinalysis test. Cf. Department of Navy v. Egan, supra, at 528 (noting that the Executive Branch generally subjects those desir*678ing a security clearance to “a background investigation that varies according to the degree of adverse effect the applicant could have on the national security”).
It is not clear, however, whether the category defined by the Service’s testing directive encompasses only those Customs employees likely to gain access to sensitive information. Employees who are tested under the Service’s scheme include those holding such diverse positions as “Accountant,” “Accounting Technician,” “Animal Caretaker,” “Attorney (All),” “Baggage Clerk,” “Co-op Student (All),” “Electric Equipment Repairer,” “Mail Clerk/Assistant,” and “Messenger.” App. 42-43. We assume these positions were selected for coverage under the Service’s testing program by reason of the incumbent’s access to “classified” information, as it is not clear that they would fall under either of the two categories we have already considered. Yet it is not evident that those occupying these positions are likely to gain access to sensitive information, and this apparent discrepancy raises in our minds the question whether the Service has defined this category of employees more broadly than is necessary to meet the purposes of the Commissioner’s directive.
We cannot resolve this ambiguity on the basis of the record before us, and we think it is appropriate to remand the case to the Court of Appeals for such proceedings as may be necessary to clarify the scope of this category of employees subject to testing. Upon remand the Court of Appeals should examine the criteria used by the Service in determining what materials are classified and in deciding whom to test under this rubric. In assessing the reasonableness of requiring tests of these employees, the court should also consider pertinent information bearing upon the employees’ privacy expectations, as well as the supervision to which these employees are already subject.
Ill
Where the Government requires its employees to produce urine samples to be analyzed for evidence of illegal drug *679use, the collection and subsequent chemical analysis of such samples are searches that must meet the reasonableness requirement of the Fourth Amendment. Because the testing program adopted by the Customs Service is not designed to serve the ordinary' needs of law enforcement, we have balanced the public interest in the Service’s testing program against the privacy concerns implicated by the tests, without reference to our usual presumption in favor of the procedures specified in the Warrant Clause, to assess whether the tests required by Customs are reasonable.
We hold that the suspicionless testing of employees who apply for promotion to positions directly involving the interdiction of illegal drugs, or to positions that require the incumbent to carry a firearm, is reasonable. The Government’s compelling interests in preventing the promotion of drug users to positions where they might endanger the integrity of our Nation’s borders or the life of the citizenry outweigh the privacy interests of those who seek promotion to these positions, who enjoy a diminished expectation of privacy by virtue of the special, and obvious, physical and ethical demands of those positions. We do not decide whether testing those who apply for promotion to positions where they would handle “classified” information is reasonable because we find the record inadequate for this purpose.
The judgment of the Court of Appeals for the Fifth Circuit is affirmed in part and vacated in part, and the case is remanded for further proceedings consistent with this opinion.
It is so ordered.
After this case was decided by .the Court of Appeals, 816 F. 2d 170 (CA5 1987), the United States Department of Health and Human Services, in accordance with recently enacted legislation, Pub. L. 100-71, § 503, 101 *662Stat. 468-471, promulgated regulations (hereinafter HHS Regulations or HHS Reg.) governing certain federal employee drug-testing programs. 53 Fed. Reg. 11979 (1988). To the extent the HHS Regulations add to, or depart from, the procedures adopted as part of a federal drug-screening program covered by Pub. L. 100-71, the HHS Regulations control. Pub. L. 100-71, § 503(b)(2)(B), 101 Stat. 470. Both parties agree that the Customs Service’s drug-testing program must conform to the HHS Regulations. See Brief for Petitioners 6, n. 8; Brief for Respondent 4-5, and n. 4. We therefore consider the HHS Regulations to the extent they supplement or displace the Commissioner’s original directive. See California Bankers Assn. v. Shultz, 416 U. S. 21, 53 (1974); Thorpe v. Housing Authority of Durham, 393 U. S. 268, 281-282 (1969).
One respect in which the original Customs directive differs from the now-prevailing regime concerns the extent to which the employee may be required to disclose personal medical information. Under the Service’s original plan, each tested employee was asked to disclose, at the time the urine sample was collected, any medications taken within the last 30 days, and to explain any circumstances under which he may have been in legitimate contact with illegal substances within the last 30 days. Failure to provide this information at this time could result in the agency not considering the effect of medications or other licit contacts with drugs on a positive test result. Under the HHS Regulations, an employee need not provide information concerning medications when he produces the sample for testing. He may instead present such information only, after he is notified that his specimen tested positive for illicit drugs, at which time the Medical Review Officer reviews all records made available by the employee to determine whether the positive indication could have been caused by lawful use of drugs. See HHS Reg. § 2.7, 53 Fed. Reg. 11985-11986 (1988).
The procedures prescribed by the Customs Service for the collection and analysis of the requisite samples do not carry the grave potential for “arbitrary and oppressive interference with the privacy and personal security of individuals,” United States v. Martinez-Fuerte, 428 U. S. 543, 554, (1976), that the Fourth Amendment was designed to prevent. Indeed, these procedures significantly minimize the program’s intrusion on privacy interests. Only employees who have been tentatively accepted for promotion or transfer to one of the three categories of covered positions are tested, and applicants know at the outset that a drug test is a requirement of those positions. Employees are also notified in advance of the scheduled sample collection, thus reducing to a minimum any “unsettling show of authority,” Delaware v. Prouse, 440 U. S. 648, 657 (1979), that may be associated with unexpected intrusions on privacy. Cf. United States v. Martinez-FueHe, supra, at 559 (noting that the intrusion on privacy occasioned by routine highway checkpoints is minimized by the fact that motorists “are not taken by surprise as they know, or may obtain knowledge of, the location of the checkpoints and will not be stopped elsewhere”); Wyman v. James, 400 U. S. 309, 320-321 (1971) (providing a welfare re-*673eipient with advance notice that she would be visited by a welfare caseworker minimized the intrusion on privacy occasioned by the visit). There is no direct observation of the act of urination, as the employee may provide a specimen in the privacy of a stall.
Further, urine samples may be examined only for the specified drugs. The use of samples to test for any other substances is prohibited. See HHS Reg. § 2.1(c), 53 Fed. Reg. 11980 (1988). And, as the Court of Appeals noted, the combination of EMIT and GC/MS tests required by the Service is highly accurate, assuming proper storage, handling, and measurement techniques. 816 F. 2d, at 181. Finally, an employee need not disclose personal medical information to the Government unless his test result is positive, and even then any such information is reported to a licensed physician. Taken together, these procedures significantly minimize the intrusiveness of the Service’s drug-screening program.
The point is well illustrated also by the Federal Government’s practice of requiring the search of all passengers seeking to board commercial airliners, as well as the search of their carry-on luggage, without any basis for suspecting any particular passenger of an untoward motive. Applying our precedents dealing with administrative searches, see, e. g., Camara v. Municipal Court of San Francisco, 387 U. S. 523 (1967), the lower courts that have considered the question have consistently concluded that such searches are reasonable under the Fourth Amendment. As Judge Friendly explained in a leading case upholding such searches:
“When the risk is the jeopardy to hundreds of human lives and millions of dollars of property inherent in the pirating or blowing up of a large airplane, that danger alone meets the test of reasonableness, so long as the search is conducted in good faith for the purpose of preventing hijacking or like damage and with reasonable scope and the passenger has been given advance notice of his liability to such a search so that he can avoid it by choosing not to travel by air.” United States v. Edwards, 498 F. 2d 496, 500 (CA2 1974) (emphasis in original).
See also United States v. Skipwith, 482 F. 2d 1272, 1275-1276 (CA5 1973); United States v. Davis, 482 F. 2d 893, 907-912 (CA9 1973). It is true, as counsel for petitioners pointed out at oral argument, that these air piracy precautions were adopted in response to an observable national and international hijacking crisis. Tr. of Oral Arg. 13. Yet we would not suppose that, if the validity of these searches be conceded, the Government would be precluded from conducting them absent a demonstration of danger as to any particular airport or airline. It is sufficient that the Government have a compelling interest in preventing an otherwise pervasive societal problem from spreading to the particular context.
Nor would we think, in view of the obvious deterrent purpose of these searches, that the validity of the Government’s airport screening program necessarily turns on whether significant numbers of putative air pirates are actually discovered by the searches conducted under the program. In the 15 years the program has been in effect, more than 9.5 billion persons have been screened, and over 10 billion pieces of luggage have been inspected. See Federal Aviation Administration, Semiannual Report to Congress on the Effectiveness of The Civil Aviation Program (Nov. 1988) (Exhibit 6). By far the overwhelming majority of those persons who have been searched, like Customs employees who have been tested under the Service’s drug-screening scheme, have proved entirely innocent — only *67642,000 firearms have been detected during the same period. Ibid. When the Government’s interest lies in deterring highly hazardous conduct, a low incidence of such conduct, far from impugning the validity of the scheme for implementing this interest, is more logically viewed as a hallmark of success. See Bell v. Wolfish, 441 U. S. 520, 559 (1979).
Indeed, petitioners’ objection is based on those features of the Service's program — the provision of advance notice and the failure of the sample collector to observe directly the act of urination — that contribute sig-*677nifieantly to diminish the program’s intrusion on privacy. See supra, at 672-673, n. 2. Thus, under petitioners’ view, “the testing program would be more likely to be constitutional if it were more pervasive and more invasive of privacy.” 816 F. 2d, at 180.