While recent studies indicate that injection drug users (IDUs) can change their behavior to reduce injection risk of HIV, it remains unclear which users are most likely to change and which mediating variables are most amenable to intervention. We report a study in which a cohort of high-risk IDUs was followed over time to determine which variables were associated with reduced injection risk of HIV. Of 317 IDUs who at baseline had shared a dirty needle in the previous 30 days, 234 (74%) were followed for 6 months. Of these, 107 (46%) reported reduced or eliminated injection risk between the baseline and follow-up interviews, 82 (35%) by not injecting and 25 (11%) by not sharing syringes. Those who attended self-help meetings between the two interviews were almost twice as likely to report reduced or eliminated risk as those who did not attend (OR= 1.92;p= 0.04). The findings suggest that, at least, IDUs in self-help groups comprise a population amenable to HIV interventions and, at most, that self-help groups may play an important role in reducing the risk of HIV in out-of-treatment populations.