Prior studies noted the perverse effects of drug law enforcement on the drug distribution system; the main source of these perverse effects is the tendency of supply-side enforcement to stimulate drug markets by increasing prices. The analysis of the London drug markets was conducted in 1995-96. Information on six markets was collected by means of structured and semi-structured interviews with market users, supplemented by interviews with drug workers and police. Two case studies were then conducted on contrasting drug markets, including a classic open market in an inner-city area with a mixture of commercial and residential buildings and a closed marked located in a traditionally white, poor, working-class area that had experienced extensive ethnic minority immigration and that had high unemployment. Results suggested the desirability of an eclectic approach that used a mix of enforcement, situational prevention, and drug treatment strategies. The main advantage of this approach would be to reduce demand without increasing the retail price of drugs. Figures, tables, footnotes, and 40 references (Author abstract modified)