U.S.-supported crop control, enforcement, and interdiction efforts in Colombia and Bolivia have not produced major reductions in coca and marijuana production and trafficking, and major reductions are not likely to be achieved in the near future. Despite large-scale efforts by the Colombian government to eradicate coca and marijuana cultivation and to interdict cocaine processing and trafficking, Colombia remains the principal source of cocaine for the U.S. market and the leading supplier of marijuana. Seemingly intractable problems including political assassinations, threats and intimidation of Colombian officials, and corruption have impeded government efforts to control the narcotics trade. Also, the United States and Colombia have not identified an effective herbicide to combat coca growth. Bolivia has no law restricting coca cultivation, and its interdiction efforts have had no significant results. To improve the effectiveness of the U.S.-supported narcotics control effort in Colombia, the General Accounting Office recommends that the Secretary of State ensure that eradication aircraft are used during the entire day and to spray early in the marijuana growing cycle, increase U.S. monitoring of marijuana eradication activities, and request the Colombian government to use all its resources, including its military force, to combat drug production and trafficking.