This project will test and evaluate the effectiveness of a comprehensive community-based strategy the builds on street outreach intervention methods as the central activity in order to contact out-of-treatment IVDUs, their sexual partners, and prostitutes for the purpose of: 1) counseling them, 2) referring them to appropriate social and health services, and 3) monitoring their needle-sharing behavior and sexual practices in ways that will prevent the spread of HIV. As a three-year demonstration, the first year will augment the pilot project established by the MCCA, which has been in operation for eleven months, expand the ethnographic studies into four new population groups of IVDUs in San Francisco and extend the studies and services to selected high-risk communities in the second largest city of the SMSA. Combined with the previously studied and served populations, these groups constitute approximately 75-90% of the out-of-treatment IVDUs in San Francisco, and will initiate similar efforts in Oakland, California, which contains the largest number of IVDUs in Alameda County.