delivered the opinion of the Court.
This case presents questions concerning the constitutional requirements for obtaining a state search warrant.
Two Houston police officers applied to a local Justice of the Peace for a warrant to search for narcotics in petitioner's home. In support of their application, the officers submitted an affidavit which, in relevant part, recited that:
“Affiants have received reliable information from a credible person and do believe that heroin, marijuana, barbiturates and other narcotics and narcotic paraphernalia are being kept at the above described premises for the purpose of sale and use contrary to the provisions of the law.” 1
The search warrant was issued.
In executing the warrant, the local police, along with federal officers, announced at petitioner’s door that they *110were police with a warrant. Upon hearing a commotion within the house, the officers forced their way into the house and seized petitioner in the act of attempting to dispose of a packet of narcotics.
At his trial in the state court, petitioner, through his attorney, objected to the introduction of evidence obtained as a result of the execution of the warrant. The objections were overruled and the evidence admitted. Petitioner was convicted of illegal possession of heroin and sentenced to serve 20 years in the state penitentiary.2 On appeal to the Texas Court of Criminal Appeals, the conviction was affirmed, 172 Tex. Cr. R. 629, 362 S. W. 2d 111, affirmance upheld on rehearing, 172 Tex. Cr. R. 631, 362 S. W. 2d 112. We granted a writ of certiorari to consider the important constitutional questions involved. 375 U. S. 812.
In Ker v. California, 374 U. S. 23, we held that the Fourth “Amendment’s proscriptions are enforced against the States through the Fourteenth Amendment,” and that “the standard of reasonableness is the same under the Fourth and Fourteenth Amendments.” Id., at 33. Although Ker involved a search without a warrant, that case must certainly be read as holding that the standard for obtaining a search warrant is likewise “the same under the Fourth and Fourteenth Amendments.”
An evaluation of the constitutionality of a search warrant should begin with the rule that “the informed and deliberate determinations of magistrates empowered to issue warrants . . . are to be preferred over the hurried action *111of officers . . . who may happen to make arrests.” United States v. Lefkowitz, 285 U. S. 452, 464. The reasons for this rule go to the foundations of the Fourth Amendment. A contrary rule “that evidence sufficient to support a magistrate’s disinterested determination to issue a search warrant will justify the officers in making a search without a warrant would reduce the Amendment to a nullity and leave the people’s homes secure only in the discretion of police officers.” Johnson v. United States, 333 U. S. 10, 14. Under such a rule “resort to [warrants] would ultimately be discouraged.” Jones v. United States, 362 U. S. 257, 270. Thus, when a search is based upon a magistrate’s, rather than a police officer’s, determination of probable cause, the reviewing courts will accept evidence of a less “judicially competent or persuasive character than would have justified an officer in acting on his own without a warrant,” ibid., and will sustain the judicial determination so long as “there was substantial basis for [the magistrate] to conclude that narcotics were probably present . . . .” Id., at 271. As so well stated by Mr. Justice Jackson:
“The point of the Fourth Amendment, which often is not grasped by zealous officers, is not that it denies law enforcement the support of the usual inferences which reasonable men draw from evidence. Its protection consists in requiring that those inferences be drawn by a neutral and detached magistrate instead of being judged by the officer engaged in the often competitive enterprise of ferreting out crime.” Johnson v. United States, supra, at 13-14.
Although the reviewing court will pay substantial deference to judicial determinations of probable cause, the court must still insist that the magistrate perform his “neutral and detached” function and not serve merely as a rubber stamp for the police.
*112In Nathanson v. United States, 290 U. S. 41, a warrant was issued upon the sworn allegation that the affiant “has cause to suspect and does believe” that certain merchandise was in a specified location. Id., at 44. The Court, noting that the affidavit “went upon a mere affirmation of suspicion and belief without any statement of adequate supporting facts,” id., at 46 (emphasis added), announced the following rule:
“Under the Fourth Amendment, an officer may not properly issue a warrant to search a private dwelling unless he can find probable cause therefor from facts or circumstances presented to him under oath or affirmation. Mere affirmance of belief or suspicion is not enough.” Id., at 47. (Emphasis added.)
The Court, in Giordenello v. United States, 357 U. S. 480, applied this rule to an affidavit similar to that relied upon here.3 Affiant in that case swore that petitioner “did receive, conceal, etc., narcotic drugs . . . with knowledge of unlawful importation . . . .” Id., at 481. The Court announced the guiding principles to be:
“that the inferences from the facts which lead to the complaint '[must] be drawn by a neutral and de*113tached magistrate instead of being judged by the officer engaged in the often competitive enterprise of ferreting out crime/ Johnson v. United States, 333 U. S. 10, 14. The purpose of the complaint, then, is to enable the appropriate magistrate . . . to determine whether the 'probable cause’ required to support a warrant exists. The Commissioner must judge for himself the persuasiveness of the facts relied on by a complaining officer to show probable cause. He should not accept without question the complainant’s mere conclusion . . . .” 357 U. S., at 486.
The Court, applying these principles to the complaint in that case, stated that:
“it is clear that it does not pass muster because it does not provide any basis for the Commissioner’s determination . . . that probable cause existed. The complaint contains no affirmative allegation that the affiant spoke with personal knowledge of the matters contained therein; it does not indicate any sources for the complainant’s belief; and it does not set forth any other sufficient basis upon which a finding of probable cause could be made.” Ibid.
The vice in the present affidavit is at least as great as in Nathanson and Giordenello. Here the “mere conclusion” that petitioner possessed narcotics was not even that of the affiant himself; it was that of an unidentified informant. The affidavit here not only “contains no affirmative allegation that the affiant spoke with personal knowledge of the matters contained therein,” it does not even contain an “affirmative allegation” that the affiant’s unidentified source “spoke with personal knowledge.” For all that appears, the source here merely suspected, believed or concluded that there were narcotics in peti*114tioner’s possession.4 The magistrate here certainly could not “judge for himself the persuasiveness of the facts relied on ... to show probable cause.” He necessarily accepted “without question” the informant’s “suspicion,” “belief” or “mere conclusion.”
Although an affidavit may be based on hearsay information and need not reflect the direct personal observations of the affiant, Jones v. United States, 362 U. S. 257, the magistrate must be informed of some of the underlying circumstances from which the informant concluded that the narcotics were where he claimed they were, and some of the underlying circumstances from which the officer concluded that the informant, whose identity need not be disclosed, see Rugendorf v. United States, 376 U. S. 528, was “credible”or his information “reliable.” 5 Other*115wise, “the inferences from the facts which lead to the complaint” will be drawn not “by a neutral and detached magistrate,” as the Constitution requires, but instead, by a police officer “engaged in the often competitive enterprise of ferreting out crime,” Giordenello v. United States, supra, at 486; Johnson v. United States, supra, at 14, or, as in this case, by an unidentified informant.
We conclude, therefore, that the search warrant should not have been issued because the affidavit did not provide a sufficient basis for a finding of probable cause and that *116the evidence obtained as a result of the search warrant was inadmissible in petitioner’s trial.
The judgment of the Texas Court of Criminal Appeals is reversed and the case remanded for proceedings not inconsistent with this opinion.
Reversed and remanded.
The record does not reveal, nor is it claimed, that any other information was brought to the attention of the Justice of the Peace. It is elementary that in passing on the validity of a warrant, the reviewing court may consider only information brought to the magistrate’s attention. Giordenello v. United States, 357 U. S. 480, 486; 79 C. J. S. 872 (collecting cases). In Giordenello, the Government pointed out that the officer who obtained the warrant “had kept petitioner under surveillance for about one month prior to the arrest.” The Court of course ignored this evidence, since it had not been brought to the magistrate’s attention. The fact that the police may have kept petitioner’s house under surveillance is thus completely irrelevant in this ease, for, in applying for the warrant, the police did not mention any surveillance. Moreover, there is no evidence in the record that a surveillance was actually set up on petitioner’s house. Officer Strickland merely testified that “we wanted to set up surveillance on the house.” If the fact and results of such a surveillance had been appropriately presented to the magistrate, this would, of course, present an entirely different case.
Petitioner was also indicted on charges of conspiring to violate the federal narcotics laws, Act of February 9, 1909, c. 100, 35 Stat. 614, § 2, as amended, 21 U. S. C. § 174; Internal Revenue Code of 1954, §7237 (b), as amended, 26 U. S. C. §7237 (b). He was found not guilty by the jury. His codefendants were found guilty and their convictions affirmed on appeal. Garcia v. United States, 315 F. 2d 679.
In Giordenello, although this Court construed the requirement of “probable cause” contained in Rule 4 of the Federal Rules of Criminal Procedure, it did so “in light of the constitutional” requirement of probable cause which that Rule implements. Id., at 485. The case also involved an arrest warrant rather than a search warrant, but the Court said: “The language of the Fourth Amendment, that ‘. . . no Warrants shall issue, but upon probable cause . . .’ of course applies to arrest as well as search warrants.” Id., at 485-486. See Ex parte Burford, 3 Cranch 448; McGrain v. Daugherty, 273 U. S. 135, 154-157. The principles announced in Giordenello derived, therefore, from the Fourth Amendment, and not from our supervisory power. Compare Jencks v. United States, 353 U. S. 657. Accordingly, under Ker v. California, 374 U. S. 23, they may properly guide our determination of “probable cause” under the Fourteenth Amendment.
To approve this affidavit would open the door to easy circumvention of the rule announced in Nathanson and Giordenello. A police officer who arrived at the “suspicion,” “belief” or “mere conclusion” that narcotics were in someone’s possession could not obtain a warrant. But he could convey this conclusion to another police officer, who could then secure the warrant by swearing that he had “received reliable information from a credible person” that the narcotics were in someone’s possession.
Such an affidavit was sustained by this Court in Jones v. United, States, 362 U. S. 257. The affidavit in that case reads as follows:
“Affidavit in Support of a U. S. Commissioners Search Warrant for Premises 1436 Meridian Place, N. W., Washington, D. C., apartment 36, including window spaces of said apartment. Occupied by Cecil Jones and Earline Richardson.
“In the late afternoon of Tuesday, August 20, 1957, I, Detective Thomas Didone, Jr. received information that Cecil Jones and Earline Richardson were involved in the illicit narcotic traffic and that they kept a ready supply of heroin on hand in the above mentioned apartment. The source of information also relates that the two aforementioned persons kept these same narcotics either on their person, under a pillow, on a dresser or on a window ledge in said apartment. The source of information goes on to relate that on many occasions the source of information has gone to said apartment and purchased narcotic drugs from the above mentioned persons and that the nar-*115eotics were secreated [sic] in the above mentioned places. The last time being August 20, 1957.
“Both the aforementioned persons are familiar to the undersigned and other members of the Narcotic Squad. Both have admitted to the use of narcotic drugs and display needle marks as evidence of same.
“This same information, regarding the illicit narcotic traffic, conducted by Cecil Jones and Earline Richardson, has been given to the undersigned and to other officers of the narcotic squad by other sources of information.
“Because the source of information mentioned in the opening paragraph has given information to the undersigned on previous occasion and which was correct, and because this same information is given by other sources does believe that there is now illicit narcotic drugs being secreated [sic] in the above apartment by Cecil Jones and Earline Richardson.
“Det. Thomas Didone, Jr., Narcotic Squad, MPDC.
“Subscribed and sworn to before me this 21 day of August, 1957.
“James F. Splain, U. S. Commissioner, D. C.” Id., at 267-268, n. 2.
Compare, e. g., Hernandez v. People,-Colo.-, 385 P. 2d 996, where the Supreme Court of Colorado, accepting a confession of error by the State Attorney General, held that a search warrant similar to the one here in issue violated the Fourth Amendment. The court said:
“Before the issuing magistrate can properly perform his official function he must be apprised of the underlying facts and circumstances which show that there is probable cause . . ...” Id., at -, 385 P. 2d, at 999.