Two main routes of heroin administration were observed: 54 percent of the sample injected heroin, while 44 percent smoked heroin. Only 8 percent did not have a single primary route of administration. The preferred route of administration changed at least once in more than a third of heroin users. Multiple transitions in route were uncommon. Different groups of heroin users were identified, including stable injectors, stable smokers, those who moved from smoking to injecting, and those who previously injected but had moved to smoking. Stable chasers characteristically had little contact with heroin subcultures. Survival analysis indicated a small but continuing risk of moving to injection. Positive associations were observed among drug dose, route by which heroin was taken, and severity of dependence. Potential relationships between severity of dependence and the following factors are examined: drug dose, administration route, diversity of passive drug sharing rates, circumstances in which heroin is used, and differences in drug sharing partner types. 37 references and 2 figures