PIP: Evidence that behavioral factors affect the spread of HIV infection, both direct and by implication from high-risk behavior in general, and a model for further research and intervention are reviewed. Measurement of prevalence of high-risk behaviors over time is essential to see whether risk is increasing or decreasing in populations. There is good evidence that AIDS education programs have controlled HIV spread among homosexual and bisexual men in San Francisco, judging by both HIV seroprevalence and that of gonococcal proctitis. These educational interventions virtually saturated the area. Other populations have failed to respond to AIDS education, particularly teens, young adults, poor, non-white, less educated, and people from other areas. 39% of AIDS cases in the U.S. are from minority groups; 50% are Black and 24% are Hispanic. Currently homosexual men living outside a gay community, those without social ties and bisexual men are still showing increasing HIV infections, while homosexual men in open, active communities have decreasing rates. Other risk-behaviors associated with HIV infection include use of drugs, alcohol, tobacco, and having sex outside of "relationships." Conditions correlated with safe behaviors included knowing of one's positive HIV status, possessing skills of safe sex, perceiving one's risk accurately, and having peer support. Peer support is extremely influential, and includes general social support, peer expectations and support for behavior change, and capability to seek help when needed. A detailed AIDS risk reduction model is proposed and described.