The Risk Avoidance Partnership (RAP) Project conducted in Hartford, Connecticut, tested a program to train active drug injectors and crack cocaine users as "Peer Health Advocates" (PHAs) to deliver a modular HIV, hepatitis, and STI prevention intervention to hard-to-reach drug users in their networks and others in the city. The intervention was designed to diffuse health promotion and risk-reduction interventions by supporting PHAs to model prevention practices and deliver risk- and harm-reduction materials and information. We compared change in behaviors and attitudes between baseline and 6-month follow-up of 112 primarily African-American and Latino PHAs, 223 of their drug-user network contact referrals, and 118 other study recruits (total n = 523). Results indicated significant HIV risk reduction among all study participants, associated with significant health advocacy action conducted by PHAs, and a relationship between exposure to the RAP peer-delivered intervention and risk reduction among all study groups. Findings suggest that active drug users' engagement in peer health advocacy can set in motion a feedback and diffusion process that supports both the continued work of the PHAs and the adoption of harm reduction and mimicking of health advocacy by their peers.