delivered the opinion of the Court.
Petitioner Eugene Kelley was seriously injured when he fell from the top of a tri-lével railroad car where he had been working. He sought recovery for his injuries from the respondent railroad under the Federal Employers’ Liability Act (FELA), 35 Stat. 65, as amended, 45 U. S. C. §§ 51-60. Under the FELA, a covered railroad is liable for negligently causing the injury or death of any person “while he is employed” by the railroad. Although petitioner acknowledged that he was technically in the employ of a trucking company rather than the railroad, he contended that his work was sufficiently under the control of the railroad to bring him within the *320coverage of the FELA. The District Court agreed, but the Court of Appeals for the Ninth Circuit reversed, 486 F. 2d 1084 (1973), creating an apparent conflict with a previous decision of the Fourth Circuit, Smith v. Norfolk & Western R. Co., 407 F. 2d 601, cert. denied, 395 U. S. 979 (1969).1 We granted certiorari to resolve the conflict. 416 U. S. 935 (1974). We vacate the judgment and remand the case for further proceedings in the District Court.
I
At the time of his accident, petitioner had worked for the Pacific Motor Trucking Co. (PMT), a wholly owned subsidiary of the Southern Pacific Co., for about eight years2 PMT was engaged in various trucking enterprises, primarily in conjunction with the railroad operations of its parent company. Among PMT’s functions was transporting new automobiles from respondent’s San Francisco railyard to automobile dealers in the San Francisco area. As part of its contractual arrangement with *321the railroad, PMT would unload automobiles from Southern Pacific’s “tri-level” auto-carrying flatcars when they arrived in the yard. It was petitioner’s job to unhook the automobiles from their places on the railroad cars and to drive them into the yard for further transfer to PMT auto trailers. PMT maintained the unloading operation in the yard on a permanent basis. Although there were Southern Pacific employees in the area who would occasionally consult with PMT employees about the unloading process, PMT supervisors controlled and directed the day-to-day operations.
On July 3, 1963, petitioner was unhooking automobiles in the usual fashion from the top level of one of the tri-level flatcars. A safety cable, normally affixed to the flatcar to protect against falls, was apparently not in place because of an equipment defect. During the unhooking process, petitioner fell from the top of the car and suffered a disabling injury. He subsequently received workmen’s compensation payments from PMT. Shortly before the three-year FELA statute of limitations had run, he brought suit against the respondent,3 claiming it had been negligent in failing to maintain the safety cable in its proper place and in proper working order.
In his complaint, petitioner alleged that he was employed by the respondent railroad within the meaning of the FELA. After a six-day hearing, the District Court, sitting as trier of fact,4 ruled in petitioner’s favor on the employment question. The job of unloading *322automobiles was the railroad’s responsibility, the court found, “pursuant to its contractual responsibilities to the shippers and its tariff responsibilities.” In addition, the court found that the railroad supplied the necessary ramps and owned the area in which the PMT employees worked. The responsibility for supervision and control of the unloading operations was respondent’s, the court concluded, even though “the exercise thereof was executed by employees of Pacific Motor Trucking Company.” In sum, the court found that PMT was serving generally as the railroad’s agent; PMT employees were agents of the railroad for the purposes of the unloading operation; and because the work being performed by petitioner was “in fulfillment of a non-delegable duty of defendant Southern Pacific Company,” the relationship between petitioner and the railroad was sufficient to bring him within the coverage of the FELA. After this resolution of the employment issue, the railroad stipulated to its negligence, the parties agreed to set damages at $200,000, and the trial court entered judgment for petitioner in that amount.
The Court of Appeals observed that the District Court had not found that petitioner was “employed” by the railroad, either permanently or at the time of his accident. The court noted that the “while employed” clause of the FELA requires a finding not just of agency but of a master-servant relationship between the rail carrier and the FELA plaintiff. Concluding that the District Court had applied an unduly broad test for FELA liability, the Court of Appeals reversed the District Court’s judgment.
II
Petitioner insists that the District Court in effect made a factual finding of employment and that the Court of Appeals erred in upsetting that finding. Of course, even *323if the District Court made such a finding of employment after applying the proper principles of law, that would not be the end of the matter. Under Fed. Rule Civ. Proc. 52 (a), an appellate court must set aside the trial court’s findings if it concludes that they are “clearly erroneous.” See United States v. United States Gypsum Co., 333 U. S. 364, 394-395 (1948). We need not reach the question whether any of the District Court’s findings in this case were clearly erroneous, however, since we agree with the Court of Appeals that the trial court applied an erroneous legal standard in holding that the plaintiff was within the reach of the FELA. United States v. Singer Mfg. Co., 374 U. S. 174, 194 n. 9 (1963).
The heart of the District Court’s analysis was its conclusion that the “traditional agency relationship” between respondent and PMT, in conjunction with the master-servant relationship between PMT and petitioner, was sufficient under the circumstances of this case to bring petitioner under the coverage of the Act. But this Court has repeatedly required more than that to satisfy the “while employed” clause of the FELA. From the beginning the standard has been proof of a master-servant relationship between the plaintiff and the defendant railroad. See Robinson v. Baltimore & Ohio R. Co., 237 U. S. 84, 94 (1915); Hull v. Philadelphia & Reading R. Co., 252 U. S. 475, 479 (1920); Baker v. Texas & Pacific R. Co., 359 U. S. 227, 228 (1959).
In an early FELA case, this Court rioted that the words “employee” and “employed” in the statute were used in their natural sense, and were “intended to describe the conventional relation of employer and employe.” Robinson, supra, at 94. In Baker, supra, the Court reaffirmed that for the purposes of the FELA the question of employment, or master-servant status, was to be determined by reference to common-law principles. The *324Court in Baker referred to sections of the Restatement (Second) of Agency dealing with the borrowed-servant doctrine and the general master-servant relationship as a guideline for analysis and proper jury instructions.5 Section 220 (1) of the Restatement defines a servant as “a person employed to perform services in the affairs of another and who with respect to the physical conduct in the performance of the services is subject to the other’s control or right to control.” In § 220 (2), the Restatement recites various factors that are helpful in applying that definition. While that section is directed primarily at determining whether a particular bilateral arrangement is properly characterized as a master-servant or independent contractor relationship, it can also be instructive in analyzing the three-party relationship between two employers and a worker.
Under common-law principles, there are basically three methods by which a plaintiff can establish his “employment” with a rail carrier for FELA purposes even while he is nominally employed by another. First, the employee could be serving as the borrowed servant of the railroad at the time of his injury. See Restatement (Second) of Agency § 227; Linstead v. Chesapeake & Ohio R. Co., 276 U. S. 28 (1928). Second, he could be deemed to be acting for two masters simultaneously. See Restatement § 226; Williams v. Pennsylvania R. Co., 313 F. 2d 203, 209 (CA2 1963). Finally, he could be a sub-servant of a company that was in turn a servant of the railroad. See Restatement § 5 (2); Schroeder v. Pennsylvania R. Co., 397 F. 2d 452 (CA7 1968).
*325Nothing in the District Court’s findings suggests that petitioner was sufficiently under the control of respondent to be either a borrowed servant of the railroad or a dual servant of the railroad and PMT.6 The District Court’s findings come closest to suggesting a subservant relationship running from the railroad through PMT to petitioner. But even that theory fails on the findings in the trial court, since those findings did not establish the master-servant relationship between respondent and PMT necessary to render petitioner a subservant of'the railroad.
The District Court found that PMT employees exercised supervision and control over the unloading operations, although the railroad bore the “responsibility” for those functions. On these facts, the District Court was plainly correct in concluding that PMT was an agent of the railroad. But a finding of agency is not tantamount to a finding of a master-servant relationship. See Restatement (Second) of Agency § 2. The finding that the railroad was “responsible” for the unloading operations is significantly weaker than would be a finding that it controlled or had the right to control the physical conduct of the PMT employees in the course of their unloading operations. The railroad would satisfy the District Court’s “responsibility” test whenever it agreed to perform a serv*326ice and subsequently engaged another company to perform that service for it on its premises. The “control or right to control” test, by contrast, would be met only if it were shown that the role of the second company was that of a conventional common-law servant.7 Accordingly, we agree with the Court of Appeals that the District Court’s test for FELA coverage was too broad.
Ill
The dissenters argue that even if the District Court erred in defining the applicable legal standard, we should reverse the Court of Appeals and reinstate the judgment of the District Court. The facts found by the District Court, they contend, satisfied the requirements of the “while employed” clause, even under the proper test. We disagree.
As we noted in Part II, the District Court’s findings concerning the contractual relationship between PMT and the railroad fall far short of compelling the conclusion that Kelley was employed by Southern Pacific. The court’s other factual determinations add no more force to the claim. The findings that Kelley’s crew worked most of the time on the railroad’s premises and that railroad employees were responsible for checking safety conditions *327on the tri-level cars reflect the fact that the activities of the two companies were closely related and necessarily had to be coordinated. Railroad employees tending the cars and PMT employees unloading them naturally had substantial contact with one another. In addition, Southern Pacific supervisory personnel were occasionally in the area where PMT conducted its unloading operations and from time to time would advise or consult with PMT employees and supervisors. But the trial court did not find that Southern Pacific employees played a significant supervisory role in the unloading operation or, more particularly, that petitioner was being supervised by Southern Pacific employees at the time of his injury.8 Nor did the court find that Southern Pacific employees had any general right to control the activities of petitioner and the other PMT workers.9
The two companies were sufficiently distinct in organization and responsibility that there was no apparent overlap in the supervisory ranks. Indeed, the labor con*328tract between the Teamsters and PMT expressly provided that the PMT employees would be subject only to the control of PMT supervisors. In light of the analysis in this Court’s previous cases, the District Court’s findings clearly fail to establish that petitioner was “employed” by the railroad.
In Robinson v. Baltimore & Ohio R. Co., supra, the petitioner was an employee of the Pullman Company, serving as porter in charge of a Pullman car that was hauled by the respondent railroad. Although the Pullman employees worked closely with railroad employees, and although the Pullman car was an integral part of the railroad operation, the Court held that that was not enough to make petitioner an employee of the railroad for the purposes of the Act. Even the petitioner’s responsibility for taking tickets or fares of passengers boarding the Pullman car at night was not enough to make him a servant of the railroad. This service was merely an accommodation to the railroad, not a demonstration of the railroad’s right to control the conduct of the Pullman employee. The Court stated that at the time the Act was passed, “[i]t was well known that there were on interstate trains persons engaged in various, services for other masters. Congress, familiar with this situation, did not use any appropriate expression which could be taken to indicate a purpose to include such persons among those to whom the railroad company was to be liable under the Act.” 237 U. S., at 94. The Pullman company, like PMT in this case, selected its own employees, and it “defined their duties, fixed and paid their wages, directed and supervised the performance of their tasks, and placed and removed them at its pleasure.” Id., at 93.
In the following year, the Court was again faced with the question whether a particular worker was an employee of the railroad that had caused his death, or whether he *329was an independent contractor. Chicago, R. I. & P. R. Co. v. Bond, 240 U. S. 449 (1916). The decedent had been engaged by the railroad to procure coal and wood and to perform various other services at its loading center in Enid, Okla. Although the railroad directed the decedent’s activities to some extent, the Court observed that those directions were simply reformulations of the flexible obligations assumed by the decedent under his contract, not “a detailed control of the actions of [decedent] or those of his employees.” Id., at 455-456. The arrangement by which decedent had been engaged to provide services for the railroad, the Court concluded, was “not the engagement of a servant submitting to subordination and subject momentarily to superintendence, but of one capable of independent action, to be judged of by its results.” Id., at 456.
In Bond the Court relied on the earlier decision in Standard Oil Co. v. Anderson, 212 U. S. 215 (1909), to clarify the distinction between a contractor and an employee. In that case, a longshoreman was injured when a winch operator negligently lowered a load of oil cases on him. Petitioner, the general employer of the negligent winchman, argued that at the time of the accident the winchman was the borrowed servant of the stevedoring company, the longshoreman’s employer. The Court, however, held that the winchman was not a servant of the stevedore but the servant of an independent contractor. The general employer had not furnished the employee to the stevedore, the Court wrote; it had furnished only the employee’s work. Focusing on the locus of the power to control and direct the servant’s work, the Court emphasized the importance of distinguishing between “authori- • tative direction and control, and mere suggestion as to details or the necessary cooperation, where the work furnished is part of a larger undertaking.” Id., at 222. Cf. *330Denton v. Yazoo & Mississippi Valley R. Co., 284 U. S. 305 (1932).
In this case, as in Anderson, the evidence of contacts between Southern Pacific employees and PMT employees may indicate, not direction or control, but rather the passing of information and the accommodation that is obviously required in a large and necessarily coordinated operation. See Del Vecchio v. Pennsylvania R. Co., 233 P. 2d 2, 5 (CA3 1956). The informal contacts between the two groups must assume a supervisory character before the PMT employees can be deemed pro hae vice employees of the railroad.10
*331The factual setting of Baker v. Team & Pacific R. Co., supra, provides an instructive contrast. Petitioner in Baker was nominally employed by a contractor who was engaged in maintenance work for the railroad. At trial, he introduced evidence to show that his work was part of the maintenance task of the railroad and that the material he was pumping into the roadbed was supplied by the railroad. Most significantly, there was evidence to show that
“a supervisor, admittedly in the employ of the railroad, in the daily course of the work exercised directive control over the details of the job performed by the individual workmen, including the precise point where the mixture should be pumped, when they should move to the next point, and the consistency of the mixture.” 359 U. S., at 228-229.
Because the evidence of control or right to control was in serious dispute, the Court held that the case must be permitted to go to the jury. As we have indicated, however, the District Court found no such day-to-day supervision that would support a finding that petitioner and his coworkers were, in effect, employees of the railroad.
IV
We part compaiiy with the Court of Appeals on the propriety of a remand. The court rendered judgment for respondent apparently because it determined that the District Court had found that there was no employment relationship, or because it had decided on its own that any such finding would have been clearly erroneous. Yet, while the District Court’s failure to adopt peti*332tioner’s proposed findings of fact relating to employment is of some significance in determining what that court deemed to be the requirements of the “while employed” clause, see n. 6, supra, it is not enough to constitute a reviewable finding that there was no master-servant relationship between petitioner and the railroad. Similarly, while the Court of Appeals may have meant to suggest that in its view the record could not support a finding of employment, that suggestion is not developed in its opinion, and we think the best course at this point is to require the trier of fact to re-examine the record in light of the proper legal standard. Accordingly, we vacate the judgment of the Court of Appeals and remand the case to that Court with instructions to remand the case to the District Court for further findings in accordance with this opinion.
Vacated and remanded.
Very similar fact situations have arisen in a number of federal and state cases. E. g., Tarboro v. Reading Co., 396 F. 2d 941 (CA3 1968), cert. denied, 393 U. S. 1027 (1969); Mazzucola v. Pennsylvania R. Co., 281 F. 2d 267 (CA3 1960); Cimorelli v. New York Central R. Co., 148 F. 2d 575 (CA6 1945); Thornton v. Norfolk & Western R. Co., 307 F. Supp. 667 (ED Va. 1969); Hunter v. Missouri-Kansas-Texas R. Co., 258 F. Supp. 20 (ND Okla. 1966); Fawcett v. Missouri Pacific R. Co., 242 F. Supp. 675 (WD La. 1963), aff’d per curiam, 347 F. 2d 233 (CA5), cert. denied, 382 U. S. 907 (1965); Valentine v. South Coast Corp., 218 F. Supp. 148 (ED La. 1963), aff’d per curiam, 334 F. 2d 244 (CA5 1964); Williams v. Chicago & Eastern Illinois R. Co., 13 Ill. App. 3d 596, 300 N. E. 2d 766 (1973); Waters v. Chicago & Eastern Illinios R. Co., 86 Ill. App. 2d 48, 229 N. E. 2d 151 (1967); Turpin v. Chicago, B. & Q. R. Co., 403 S. W. 2d 233 (Mo.), cert. denied, 384 U. S. 1003 (1966); Drago v. Central R. Co., 93 N. J. L. 176, 106 A. 803, cert. denied, 251 U. S. 553 (1919).
Petitioner has abandoned his claim that PMT’s status as respondent’s wholly owned subsidiary should render respondent liable generally for injuries to PMT employees.
In most FELA cases a finding of nonemployment does no more than deprive the plaintiff of the various procedural and proof advantages of the Act, since the common-law negligence action against a nonemployer is generally available in the alternative. In this case, however, when petitioner brought his FELA suit, the statute of limitations for California’s common-law negligence action had already run.
Although both parties initially demanded a jury trial, they agreed to try the limited question of employment to the court.
A year later, in Ward v. Atlantic Coast Line R. Co., 362 U. S. 396, 400 (1960), the Court again cited the Restatement as the proper basis for instructing a jury on the various factors that bear on the factual question of employment. The Court in Ward approved an instruction that incorporated several of the factors mentioned in Restatement §220.
It appears that the District Court consciously declined to malee a finding of “employment” or master-servant relationship between the railroad and Kelley. Petitioner proposed findings that respondent “had the right to exercise control over the details of the work being performed by [petitioner],” that the parties “believed that a relationship of- master and servant existed” between them, and that petitioner “was an ‘employee’ of defendant Southern Pacific Company.” The court declined to make any of these three proposed findings, although it adopted several of petitioner’s less critical proposed findings in whole or in part. Moreover, the court specifically found that at the time of his injury, petitioner was in the employment of PMT, a finding that petitioner, of course, had not requested.
The District Court appeared to place substantial weight on its finding that the unloading operation was a “non-delegable duty” of the railroad, “pursuant to its contractual responsibilities to the shippers and its tariff responsibilities.” But the fact that respondent undertook the contractual obligation to unload the cars and added the unloading cost to its overall charge to the shipper does not affect the nature of its arrangement with PMT. The railroad was free either to use its own employees to unload the automobiles or to subcontract the work to another company. Nor did the publication of tariffs for the unloading services automatically render anyone who performed those tasks an employee of the railroad for FELA purposes. See Norman v. Spokane-Portland & S. R. Co., 101 F. Supp. 350 (Ore. 1950), aff'd per curiam, 192 F. 2d 1020 (CA9 1951).
Petitioner has pointed to testimony from PMT employees who stated that in the course of the unloading operation they had contact with various Southern Pacific employees, including clerks, who would check on arriving and departing cars, “car-whackers,” who were responsible for car maintenance and inspection, and switchmen, who would occasionally ask the PMT employees to indicate when they were finished working on a ear so that the switch engine could clear the tracks. These contacts, however, were plainly not supervisory in nature and do not buttress petitioner’s claim to railroad employment.
In addition to the findings discussed above, the District Court found that petitioner had worked for PMT for a substantial period, that he performed unskilled labor, and that he was compensated by an hourly wage. While these factors are generally relevant to the employment inquiry, see Restatement (Second) of Agency §§220 (2) (d), (f), (g), we fail to see how they aid petitioner here. They make it plain that Kelley was a general servant of PMT, but neither the District Court nor the dissenters explain how they bear significantly on respondent’s control over or right to control Kelley’s activities.
The Court in Shenker v. Baltimore & Ohio R. Co., 374 U. S. 1 (1963), applied the analysis of Standard Oil Co. v. Anderson, 212 U. S. 215 (1909), in a factual setting somewhat analogous to that of the present case. The petitioner in-Shenker was employed as a janitor for the B&O Railroad. In addition to his work for the B&O, he maintained a nearby rail station and performed various services for the Pittsburgh & Lake Erie Railroad (P&LE). Although petitioner was on P&LE’s premises and was doing P&LE's work when he was injured, the Court noted that “there can be no question that the petitioner is an employee of the B&O.” 374 U. S., at 5. Citing Anderson, the Court wrote:
“[U]nder the common law loaned-servant doctrine immediate control and supervision is critical in determining for whom the servants are performing services. In the present case, the undisputed facts show that the petitioner was at all times paid by the B&O and under the sole supervision of B&O employees. The intimations of the B&O that the petitioner might have been given directions by the P&LE baggageman is at most an example of the minimum cooperation necessary to carry out a coordinated undertaking, and, as noted in Anderson, cannot amount to control or supervision.” Id., at 6 (footnote omitted).
Accord, Hull v. Philadelphia & Reading R. Co., 252 U. S. 475, 479-480 (1920). In Linstead v. Chesapeake & Ohio R. Co., 276 U. S. 28 (1928), the Court held that the borrowed-servant test was met where an employer had made the services of several of its employees available to the C&O Railroad for a specific purpose. Linstead, a conductor employed by the Big Four Railroad was instructed to *331accompany a C&O train along C&O tracks between-Kentucky and Ohio, under the immediate supervision of a C&O trainmaster. On these facts the Court held that he was the “special employee” of the C&O and could recover from the railroad under the FELA.