This article describes social capital in a cohort of 227 Mexican American men who are long-term injection heroin users. Social capital scores for current and former users were similar, suggesting equal absolute values of capital, but associated with illicit activities in current users and with cessation efforts in former users. Stable drug-using relationships provided high negative capital, whereas conventional relationships provided positive capital. Thus, social capital functions dichotomously in positive and negative contextualized roles. This study provides an alternative understanding of the dynamic interactions between individuals, environment, and drug abuse and can inform prevention and treatment interventions for an important demographic group.