The report provides illegal heroin, cocaine, marijuana, hallucinogen, depressant, and stimulant prices. In addition, purity levels are included for cocaine and heroin as is the delta-9-tetrahydrocannabinol (THC) potency for marijuana. Highlights of the report include: (1) Cocaine remained readily available in all major US metropolitan areas from January through September 1991. The national price range for cocaine remained stable, but prices diminished in the overwhelming majority of principal US cities; (2) Cocaine purity at kilogram, ounce, and gram levels increased during that same period; (3) Trending based upon heroin prices and purities is less clearly defined than other drugs of abuse in this report, the result of numerous and diverse foreign sources of supply and extremes in purity levels evident at both wholesale and retail levels; and (4) Marijuana prices in Hawaii and Maine increased during July-September 1991 because of diminished availability. Footnotes, tables