opinion: Mr. Justice Whittaker
  delivered the opinion of the Court.
  Petitioner was convicted of knowingly concealing and transporting narcotic drugs in Denver, Colorado, in violation of 35 Stat. 614, as amended, 21 U. S. C. § 174. His conviction was based in part on the use in evidence against him of two “envelopes containing [865 grains of] heroin” and a hypodermic syringe that had been taken from his person, following his arrest, by the arresting officer. Before the trial, he moved to suppress that evidence as having been secured through an unlawful search and seizure. After hearing, the District Court found that the arresting officer had probable cause to arrest petitioner without a warrant and that the subsequent search and seizure were therefore incident to a lawful arrest, and overruled the motion to suppress. 146 F. Supp. 689. At the subsequent trial, that evidence was offered and, over petitioner’s renewed objection, was received in evidence, and the trial resulted, as we have said, in petitioner’s conviction. The Court of Appeals affirmed the conviction, 248 F. 2d 295, and certiorari was sought on the sole ground that the search and seizure violated the Fourth Amendment and therefore the use of the heroin in evidence vitiated the conviction. We granted the writ to determine that question. 357 U. S. 935.
  The evidence offered at the hearing on the motion to suppress was not substantially disputed. It established that one Marsh, a federal narcotic agent with 29 years’ experience, was stationed at Denver; that one Hereford had been engaged as a “special employee” of the Bureau of Narcotics at Denver for about six months, and from time to time gave information to Marsh regarding violations of the narcotic laws, for which Hereford was paid small sums of money, and that Marsh had always found the information given by Hereford to be accurate and reliable. On September 3, 1956, Hereford told Marsh that James Draper (petitioner) recently had taken up abode at a stated address in Denver and “was peddling narcotics to several addicts” in that city. Four days later, on September 7, Hereford told Marsh “that Draper had gone to Chicago the day before [September 6] by train [and] that he was going to bring back three ounces of heroin [and] that he would return to Denver either on the morning of the 8th of September or the morning of the 9th of September also by train.” Hereford also gave Marsh a detailed physical description of Draper and of the clothing he was wearing, and said that he would be carrying “a tan zipper bag,” and that he habitually “walked real fast.”
  On the morning of September 8, Marsh and a Denver police officer went to the Denver Union Station and kept watch over all incoming trains from Chicago, but they did not see anyone fitting the description that Hereford had given. Repeating the process on the morning of September 9, they saw a person, having the exact physical attributes and wearing the precise clothing described by Hereford, alight from an incoming Chicago train and start walking “fast” toward the exit. He was carrying a tan zipper bag in his right hand and the left was thrust in his raincoat pocket. Marsh, accompanied by the police officer, overtook, stopped and arrested him. They then searched him and found the two “envelopes containing heroin” clutched in his left hand in his raincoat pocket, and found the syringe in the tan zipper bag. Marsh then took him (petitioner) into custody. Hereford died four days after the arrest and therefore did not testify at the hearing on the motion.
  26 U. S. C. (Supp. V) § 7607, added by § 104 (a) of the Narcotic Control Act of 1956, 70 Stat. 570, provides, in pertinent part:
  “The Commissioner . . . and agents, of the Bureau of Narcotics . . . may—
  “(2) make arrests without warrant for violations of any law of the United States relating to narcotic drugs . . . where the violation is committed in the presence of the person making the arrest or where such person has reasonable grounds to believe that the person to be arrested has committed or is committing such violation.”
  The crucial question for us then is whether knowledge of the related facts and circumstances gave Marsh “probable cause” within the meaning of the Fourth Amendment, and “reasonable grounds” within the meaning of § 104 (a), supra, to believe that petitioner had committed or was committing a violation of the narcotic laws. If it did, the arrest, though without a warrant, was lawful and the subsequent search of petitioner’s person and the seizure of the found heroin were validly made incident to a lawful arrest, and therefore the motion to suppress was properly overruled and the heroin was competently received in evidence at the trial. Weeks v. United States, 232 U. S. 383, 392; Carroll v. United States, 267 U. S. 132, 158; Agnello v. United States, 269 U. S. 20, 30; Giordenello v. United States, 357 U. S. 480, 483.
  Petitioner does not dispute this analysis of the question for decision. Rather, he contends (1) that the information given by Hereford to Marsh was “hearsay” and, because hearsay is not legally competent evidence in a criminal trial, could not legally have been considered, but should have been put out of mind, by Marsh in assessing whether he had “probable cause” and “reasonable grounds” to arrest petitioner without a warrant, and (2) that, even if hearsay could lawfully have been considered, Marsh’s information should be held insufficient to show “probable cause” and “reasonable grounds” to believe that petitioner had violated or was violating the narcotic laws and to justify his arrest without a warrant.
  Considering the first contention, we find petitioner entirely in error. Brinegar v. United States, 338 U. S. 160, 172-173, has settled the question the other way. There, in a similar situation, the convict contended “that the factors relating to inadmissibility of the evidence [for] purposes of proving guilt at the trial, deprive[d] the evidence as a whole of sufficiency to show probable cause for the search . . . .” Id., at 172. (Emphasis added.) But this Court, rejecting that contention, said: “[T]he so-called distinction places a wholly unwarranted emphasis upon the criterion of admissibility in evidence, to prove the accused’s guilt, of the facts relied upon to show probable cause. That emphasis, we think, goes much too far in confusing and disregarding the difference between what is required to prove guilt in a criminal case and what is required to show probable cause for arrest or search. It approaches requiring (if it does not in practical effect require) proof sufficient to establish guilt in order to substantiate the existence of probable cause. There is a large difference between the two things to be proved [guilt and probable cause], as well as between the tribunals which determine them, and therefore a like difference in the quanta and modes of proof required to establish them.” 338 U. S., at 172-173.
  Nor can we agree with petitioner’s second contention that Marsh’s information was insufficient to show probable cause and reasonable grounds to believe that petitioner had violated or was violating the narcotic laws and to justify his arrest without a warrant. The information given to narcotic agent Marsh by “special employee” Hereford may have been hearsay to Marsh, but coming from one employed for that purpose and whose information had always been found accurate and reliable, it is clear that Marsh would have been derelict in his duties had he not pursued it. And when, in pursuing that information, he saw a man, having the exact physical attributes and wearing the precise clothing and carrying the tan zipper bag that Hereford had described, alight from one of the very trains from the very place stated by Hereford and start to walk at a “fast” pace toward the station exit, Marsh had personally verified every facet of the information given him by Hereford except whether petitioner had accomplished his mission and had the three ounces of heroin on his person or in his bag. And surely, with every other bit of Hereford's information being thus personally verified, Marsh had “reasonable grounds” to believe that the remaining unverified bit of Hereford's information — that Draper would have the heroin with him — was likewise true.
  “In dealing with probable cause, ... as the very name implies, we deal with probabilities. These are not technical; they are the factual and practical considerations of everyday life on which reasonable and prudent men, not legal technicians, act.” Brinegar v. United States, supra, at 175. Probable cause exists where “the facts and circumstances within [the arresting officers’] knowledge and of which they had reasonably trustworthy information [are] sufficient in themselves to warrant a man of reasonable caution in the belief that” an offense has been or is being committed. Carroll v. United States, 267 U. S. 132, 162.
  We believe that, under the facts and circumstances here, Marsh had probable cause and reasonable grounds to believe that petitioner was committing a violation of the laws of the United States relating to narcotic drugs at the time he arrested him. The arrest was therefore lawful, and the subsequent search and seizure, having been made incident to that lawful arrest, were likewise valid. It follows that petitioner’s motion to suppress was properly denied and that the seized heroin was competent evidence lawfully received at the trial.
  Affirmed.
  The Chief Justice and Mr. Justice Frankfurter took no part in the consideration or decision of this case.
  The Fourth Amendment of the Constitution of the United States provides: “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”
  Hereford told Marsh that Draper was a Negro of light brown complexion, 27 years of age, 5 feet 8 inches tall, weighed about 160 pounds, and that he was wearing a light colored raincoat, brown slacks and black shoes.
  The terms “probable cause” as used in the Fourth Amendment and “reasonable grounds” as used in § 104 (a) of the Narcotic Control Act, 70 Stat. 570, are substantial equivalents of the same meaning. United States v. Walker, 246 F. 2d 519, 526 (C. A. 7th Cir.); cf. United States v. Bianco, 189 F. 2d 716, 720 (C. A. 3d Cir.).
  In United States v. Heitner, 149 F. 2d 105, 106 (C. A. 2d Cir.), Judge Learned Hand said “It is well settled that an arrest may be made upon hearsay evidence; and indeed, the ‘reasonable cause’ necessary to support an arrest cannot demand the same strictness of proof as the accused’s guilt upon a trial, unless the powers of peace officers are to be so cut down that they cannot possibly perform their duties.”
  Grau v. United States, 287 U. S. 124, 128, contains a dictum that “A search warrant may issue only upon evidence which would be competent in the trial of the offense before a jury (Giles v. United States, 284 Fed. 208; Wagner v. United States, 8 F. (2d) 581) . . . .” But the principles underlying that proposition were thoroughly discredited and rejected in Brinegar v. United States, supra, 338 U. S., at 172-174, and notes 12 and 13. There are several cases in the federal courts that followed the now discredited dictum in the Grau case, Simmons v. United States, 18 F. 2d 85, 88; Worthington v. United States, 166 F. 2d 557, 564-565; cf. Reeve v. Howe, 33 F. Supp. 619, 622; United States v. Novero, 58 F. Supp. 275, 279, but the great weight of authority is the other way. See, e. g., Wrightson v. United States, 236 F. 2d 672 (C. A. D. C. Cir.); United States v. Heitner, supra (C. A. 2d Cir.); United States v. Bianco, 189 F. 2d 716 (C. A. 3d Cir.); Wisniewski v. United States, 47 F. 2d 825 (C. A. 6th Cir.); United States v. Walker, 246 F. 2d 519 (C. A. 7th Cir.); Mueller v. Powell, 203 F. 2d 797 (C. A. 8th Cir.). And see Note, 46 Harv. L. Rev. 1307, 1310-1311, criticizing the Grau dictum.
  To the same effect are: Husty v. United States, 282 U. S. 694, 700-701; Dumbra v. United States, 268 U. S. 435, 441; Steele v. United States No. 1, 267 U. S. 498, 504-505; Stacey v. Emery, 97 U. S. 642, 645; Brinegar v. United States, supra, at 175, 176.
  Weeks v. United. States, 232 U. S. 383, 392; Carroll v. United States, 267 U. S. 132, 158; Agnello v. United States, 269 U. S. 20, 30; Giordenello v. United States, 357 U. S. 480, 483.