The sources of complaints received by the Division of Drug Control from July 1984 to August 1986 were tabulated by zip codes (822 complaints). Duplicate prescription data from January 1985 to December 1985 were also tabulated by zip code. Rhode Island law requires pharmacists dispensing controlled substances in Schedule II to deliver to the Division of Drug Control all duplicate copies of prescriptions for such controlled substances. The study obtained information from ARCOS, the Drug Enforcement Administration's automated record system of controlled substances distributed to all registrants (practitioners and vendors). These data were tabulated by zip code. The comparison of complaints and duplicate prescription forms in a zip code area with the data on drugs distributed to registrants in the area can reveal massive drug diversion from legitimate dispensing channels. A large number of drug complaints and registrant purchases without commensurate legitimate prescriptions and dispensing warrants monitoring and prevention efforts in the involved zip code area. 4 tables and 4 charts.