Treasury and Customs officials indicate that the amount of currency being smuggled out of the United States cannot be determined and that a sound basis for estimates is difficult to establish primarily because of the clandestine nature of smuggling. While estimates vary, law enforcement officials interviewed by GAO report a substantial amount of currency smuggling. They note that smugglers use various techniques and conveyances and that smuggling currency is relatively easy. Faced with difficulties in laundering money domestically, many individuals take currency and other negotiable instruments to other countries where it can be put into the flow of commerce and then returned to the United States under an air of legitimacy. While the Customs Service has traditionally focused on inspecting the flow of persons and cargo into the United States, its Operation Buckstop Program is specifically aimed at selectively inspecting passengers and cargo leaving the country to ensure that currency being transported outside the United States is reported. In addition, the Customs Service has increased the oversight and emphasis given currency interdiction efforts on a nationwide basis. Additional information on the districts and ports visited by GAO and on Customs currency and monetary instrument seizures is appended. Footnotes, tables, and figures