The review of heroin trends in the United States includes examination of relevant data on heroin prevalence estimates and spread in other countries, and examination of recently published clinical and epidemiological literature on heroin abuse for clues to needed action by researchers, planners, and policy makers. Recent national indicators of heroin use suggest an endemic pattern, i.e., use is widespread but incidence of new cases is presumed to be relatively low. In contrast, Drug Abuse Warning Network data from 1978 to 1992 reveal a fourfold increase in the number of heroin-related emergency room episodes. The authors discuss: the incidence of heroin use in foreign countries and the limitations of data sources; the connection between HIV and heroin; and theories of heroin epidemics (social and deviance theory, economic concept of supply and demand, and others). The authors see the potential for a rapid increase in quality and quantity of heroin in the United States from expanded Colombian production, and suggest the need to plan for a rapid-treatment outreach and law enforcement response. Table, references