Data were gathered via interviews, site visits, and examination of official records. Results indicate that relatively small proportions of cocaine, marijuana, and other illicit drugs are seized by drug interdiction agencies, and that these substances remain widely available. Reasons for the Government's inability to stop illegal drug smuggling include gaps in the interdiction system's coverage, a lack of timely and accurate tactical intelligence, and high profits that encourage smugglers to continue their activities. In addition, drug seizures are small compared to total drug imports. Finally, smugglers use methods and tactics that exploit gaps in the system's coverage and other weaknesses such as inadequate security over interdiction plans and operations. Tables and figures.