Strategies for reaching intravenous drug users (IVDUs) not in treatment and reducing risk behaviors are urgently needed to reduce the human immunodeficiency virus (HIV) epidemic. Of special concern is the need to detect which types of risk behaviors are more likely to change and which are resistant to change. The present paper analyzes changes occurring in HIV transmission risk behaviors among 778 IVDUs not in treatment, in the city of San Juan, Puerto Rico. Results show discontinuation rates of risk behaviors to be substantial. Discontinuation rates of injection equipment sharing practices varied from 33% in shared use of cookers to 74.2% in sharing needles with strangers. Drug injection and use of shooting galleries were also reduced, although to a lesser extent (8.5% and 19.3% respectively). Among protective behaviors, use of new needles was found to increase nearly twice as much as the use of bleach (20.6% vs. 11.3% respectively). The results suggest the need to understand the factors facilitating/inhibiting change in specific behaviors and the need to study the stability of these changes over longer periods of time.