formally under arrest. By 4:10 a. m. respondent had passed 6 similar balloons; over the next four days she passed 88 balloons containing a total of 528 grams of 80% pure cocaine hydrochloride.

After a suppression hearing the District Court admitted the cocaine in evidence against respondent. She was convicted of possession of cocaine with intent to distribute, 21 U. S. C. §841(a)(1), and unlawful importation of cocaine, 21 U. S. C. §§ 952(a), 960(a).

A divided panel of the United States Court of Appeals for the Ninth Circuit reversed respondent's convictions. The court noted that customs inspectors had a "justifiably high level of official skepticism" about respondent's good motives, but the inspectors decided to let nature take its course rather than seek an immediate magistrate's warrant for an x ray. 731 F. 2d, at 1372. Such a magistrate's warrant required a "clear indication" or "plain suggestion" that the traveler was an alimentary canal smuggler under previous decisions of the Court of Appeals. See United States v. QuinteroCastro, 705 F. 2d 1099 (CA9 1983); United States v. MendezJimenez, 709 F. 2d 1300, 1302 (CA9 1983); but cf. South Dakota v. Opperman, 428 U. S. 364, 370, n. 5 (1976). The court applied this required level of suspicion to respondent's case. The court questioned the "humanity" of the inspectors' decision to hold respondent until her bowels moved, knowing that she would suffer "many hours of humiliating discomfort" if she chose not to submit to the x-ray examination. The court concluded that under a "clear indication" standard "the evidence available to the customs officers when they decided to hold [respondent] for continued observation was insufficient to support the 16-hour detention." 731 F. 2d, at 1373.

The Government contends that the customs inspectors reasonably suspected that respondent was an alimentary canal smuggler, and this suspicion was sufficient to justify the detention. In support of the judgment below respondent

argues, inter alia, that reasonable suspicion would not support respondent's detention, and in any event the inspectors did not reasonably suspect that respondent was carrying narcotics internally.

The Fourth Amendment commands that searches and seizures be reasonable. What is reasonable depends upon all of the circumstances surrounding the search or seizure and the nature of the search or seizure itself. New Jersey v. T. L. O., 469 U. S. 325, 337-342 (1985). The permissibility of a particular law enforcement practice is judged by "balancing its intrusion on the individual's Fourth Amendment interests against its promotion of legitimate governmental interests." United States v. Villamonte-Marquez, 462 U. S. 579, 588 (1983); Delaware v. Prouse, 440 U. S. 648, 654 (1979); Camara v. Municipal Court, 387 U. S. 523 (1967).

Here the seizure of respondent took place at the international border. Since the founding of our Republic, Congress has granted the Executive plenary authority to conduct routine searches and seizures at the border, without probable cause or a warrant, in order to regulate the collection of duties and to prevent the introduction of contraband into this country. See United States v. Ramsey, 431 U. S. 606, 616-617 (1977), citing Act of July 31, 1789, ch. 5, 1 Stat. 29. This Court has long recognized Congress' power to police entrants at the border. See Boyd v. United States, 116 U. S. 616, 623 (1886). As we stated recently:

"Import restrictions and searches of persons or packages at the national border rest on different considerations and different rules of constitutional law from domestic regulations. The Constitution gives Congress broad comprehensive powers "[t]o regulate Commerce with foreign Nations," Art. I, §8, cl. 3. Historically such broad powers have been necessary to prevent smuggling and to prevent prohibited articles from

entry." Ramsey, supra, at 618-619, quoting United States v. 12 200-Ft. Reels of Film, 413 U. S. 123, 125 (1973).

Consistently, therefore, with Congress' power to protect the Nation by stopping and examining persons entering this country, the Fourth Amendment's balance of reasonableness is qualitatively different at the international border than in the interior. Routine searches of the persons and effects of entrants are not subject to any requirement of reasonable suspicion, probable cause, or warrant,' and first-class mail may be opened without a warrant on less than probable cause, Ramsey, supra. Automotive travelers may be stopped at fixed checkpoints near the border without individualized suspicion even if the stop is based largely on ethnicity, United States v. Martinez-Fuerte, 428 U. S. 543, 562-563 (1976), and boats on inland waters with ready access to the sea may be hailed and boarded with no suspicion whatever. United States v. Villamonte-Marquez, supra.

These cases reflect longstanding concern for the protection of the integrity of the border. This concern is, if anything, heightened by the veritable national crisis in law enforcement caused by smuggling of illicit narcotics, see United States v. Mendenhall, 446 U. S. 544, 561 (1980) (POWELL, J., concurring), and in particular by the increasing utilization of alimentary canal smuggling. This desperate practice appears to be a relatively recent addition to the smugglers' repertoire of deceptive practices, and it also appears to be exceedingly dif

'See United States v. Ramsey, 431 U. S., at 616-619; Almeida-Sanchez v. United States, 413 U. S. 266, 272–273 (1973); id., at 288 (WHITE, J., dissenting). As the Court stated in Carroll v. United States, 267 U. S. 132, 154 (1925):

"Travellers may be so stopped in crossing an international boundary 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."

ficult to detect.2 Congress had recognized these difficulties. Title 19 U. S. C. § 1582 provides that "all persons coming into the United States from foreign countries shall be liable to detention and search authorized. . . [by customs regulations]." Customs agents may "stop, search, and examine" any "vehicle, beast or person" upon which an officer suspects there is contraband or "merchandise which is subject to duty." §482; see also §§ 1467, 1481; 19 CFR §§ 162.6, 162.7 (1984).

Balanced against the sovereign's interests at the border are the Fourth Amendment rights of respondent. Having presented herself at the border for admission, and having subjected herself to the criminal enforcement powers of the Federal Government, 19 U. S. C. § 482, respondent was entitled to be free from unreasonable search and seizure. But not only is the expectation of privacy less at the border than in the interior, see, e. g., Carroll v. United States, 267 U. S.

'See United States v. DeMontoya, 729 F. 2d 1369 (CA11 1984) (required surgery; swallowed 100 cocaine-filled condoms); United States v. Pino, 729 F. 2d 1357 (CA11 1984) (required surgery; 120 cocaine-filled pellets); United States v. Mejia, 720 F. 2d 1378 (CA5 1983) (75 balloons); United States v. Couch, 688 F. 2d 599, 605 (CA9 1982) (36 capsules); United States v. Quintero-Castro, 705 F. 2d 1099 (CA9 1983) (120 balloons); United States v. Saldarriaga-Marin, 734 F. 2d 1425 (CA11 1984); United States v. Vega-Barvo, 729 F. 2d 1341 (CA11 1984) (135 condoms); United States v. Mendez-Jimenez, 709 F. 2d 1300 (CA9 1983) (102 balloons); United States v. Mosquera-Ramirez, 729 F. 2d 1352 (CA11 1984) (95 condoms); United States v. Castrillon, 716 F. 2d 1279 (CA9 1983) (83 balloons); United States v. Castaneda-Castaneda, 729 F. 2d 1360 (CA11 1984) (2 smugglers; 201 balloons); United States v. Caicedo-Guarnizo, 723 F.2d 1420 (CA9 1984) (85 balloons); United States v. Henao-Castano, 729 F.2d 1364 (CA11 1984) (85 condoms); United States v. Ek, 676 F. 2d 379 (CA9 1982) (30 capsules); United States v. Padilla, 729 F. 2d 1367 (CA11 1984) (115 condoms); United States v. Gomez-Diaz, 712 F. 2d 949 (CA5 1983) (69 balloons); United States v. D'Allerman, 712 F. 2d 100 (CA5 1983) (80 balloons); United States v. Contento-Pachon, 723 F. 2d 691 (CA9 1984) (129 balloons).

132, 154 (1925); cf. Florida v. Royer, 460 U. S. 491, 515 (1983) (BLACKMUN, J., dissenting), the Fourth Amendment balance between the interests of the Government and the privacy right of the individual is also struck much more favorably to the Government at the border. Supra, at 538.

We have not previously decided what level of suspicion would justify a seizure of an incoming traveler for purposes other than a routine border search. Cf. Ramsey, 431 U. S., at 618, n. 13. The Court of Appeals held that the initial detention of respondent was permissible only if the inspectors possessed a "clear indication" of alimentary canal smuggling. 731 F. 2d, at 1372, citing United States v. Quintero-Castro, 705 F. 2d 1099 (CA9 1983); cf. United States v. MendezJimenez, 709 F. 2d 1300 (CA9 1983). This "clear indication" language comes from our opinion in Schmerber v. California, 384 U. S. 757 (1966), but we think that the Court of Appeals misapprehended the significance of that phrase in the context in which it was used in Schmerber. The Court of Appeals viewed "clear indication" as an intermediate standard between "reasonable suspicion" and "probable cause." See Mendez-Jimenez, supra, at 1302. But we think that the words in Schmerber were used to indicate the necessity for particularized suspicion that the evidence sought might be found within the body of the individual, rather than as enunciating still a third Fourth Amendment threshold between "reasonable suspicion" and "probable cause."

No other court, including this one, has ever adopted Schmerber's "clear indication" language as a Fourth Amendment standard. See, e. g., Winston v. Lee, 470 U. S. 753,

8 In that case we stated:

"The interests in human dignity and privacy which the Fourth Amendment protects forbid any such intrusion [beyond the body's surface] on the mere chance that desired evidence might be obtained. In the absence of a clear indication that in fact such evidence will be found, these fundamental human interests require law officers to suffer the risk that such evidence may disappear unless there is an immediate search." 384 U. S., at

769-770.