The research, based on case studies of the emergence and spread of crack in Manhattan and Los Angeles and the introduction of "ice" (crystal methamphetamine in smokable form) in Hawaii, shows that frequent community monitoring, coupled with cooperation among law enforcement agencies, has the potential to break up drug markets before they are fully established. After examining stages in the development of drug use patterns, the paper presents the sources of information on drug use patterns by stage of development. The stages of development are isolated endemic use, initial grassroots switches in drug used, local coalescence of opinion about the drug and spread in use, accelerated grassroots distribution by drug dealers, precipitous increases in use, and epidemic use and system overload. Sources and types of information are anthropological and ethnographic information, street information, practical information from outreach workers and drug treatment counselors, physical symptoms and medical evidence, local law enforcement information, survey information, and media reports. The case studies show the need to act cooperatively at an early stage in a drug's rise in popularity, first to gather and analyze interdisciplinary information and then to implement drug-reduction strategies. This paper outlines ways in which local officials and agencies can combine their efforts to stem drug epidemics in their communities. 1 figure, 9 notes, and 13 references