Based on 3 years of research, including interviews and extended ethnographic fieldwork, the study used data on drug-use, risk practices, crime, and policing to examine the relationship between law enforcement and harm minimization. Findings suggest that the "successes" of police crackdowns and their impact on drug markets (including threats to public health and community safety as a result of geographical, social, and substance displacement) may be won at substantial costs, raising doubts as to their value. As a consequence of intensified law enforcement practices, drug market participants adopt risky practices in storing, transferring, and administering heroin. The illegal activity is not suppressed, but the threat of intermittent law enforcement encourages the development of a level of organization that protects participants and increases the potential for police corruption. Geographical, social, substance, and temporal displacement may occur, and relations between police and ethnic minorities may deteriorate. Once it is accepted that suppression of an activity is impossible, the task of policing is to determine the kinds of drug markets that do the least harm. This can only be ascertained by empirical research. Following the determination of the kinds of drug markets that do the least harm, police must formulate policies that will push drug markets in this direction. 2 tables and 72 references