The analysis focused on the status of the Northern Border Response Force program, problems encountered in implementing it, and future plans to expand drug interdiction activities in Mexico and neighboring Latin American countries. Results revealed that the concept of mobile bases has not become a viable operation, and the majority of drug trafficking flights continue to cross Mexico successfully. Drug traffickers responded to the program's initial success in northern Mexico by moving their operations into central and southern Mexico. The program's implementation has experienced numerous problems since its inception. These include delays due to prolonged negotiations of military assistance agreements, equipment incompatibility and the lack of communication capability between aircraft and ground forces, and Mexico's longstanding problems in retaining the required number of qualified helicopter pilots and mechanics. United States and Mexican officials plan to expand the program to include land and sea operations to respond to the changing tactics of drug traffickers. The UH-1H helicopters the United States provided have not been used for interdiction as originally intended and the concept of mobile operating bases does not appear to be suitable for the changing drug trafficker tactics. Therefore, the General Accounting Office recommends that the Secretary of State reevaluate the need to continue to lease the helicopter fleet to the government of Mexico. Figure, tables, maps, footnotes, and appended background information