The proposed prospective study seeks to: (a) develop, implement, and test a modified case management model in two neighborhoods in San Francisco and compare that model to a standard intervention already established; (b) determine the seroincidence and seroprevalence of HIV in four neighborhoods: Bayview-Hunter's Point and the Tenderloin areas of San Francisco and two high-risk neighborhoods in Oakland, California; (c) distinguish between multiple sources of information and examine 'dose' related effects of multiple interventions; and (d) using ethnographictechniques, explore the phenomenon of compliance with needle and sexual hygiene and initiation into drug using practices. Intravenous drug users (IVDUS) will be recruited in two sites in San Francisco and two in Oakland. Three hundred respondents will be recruited into the study in each site in San Francisco, and 150 in each site in Oakland. Standard instruments (AIA/AFA) will be used to assess medical history, drug use profiles, sexual history, needle-sharing and hygiene, knowledge, and attitudes, and beliefs regarding AIDS. Blood samples will be obtained and analyzed for HIV antibodies. In the two San Francisco neighborhoods, random assignment to standard or enhanced interventions will be effected, and respondents followed at six month intervals. We will compensate for the anticipated six-month 25% drop-out rate by recruiting additional research subjects for AIA assessment and random assignment. Thus, the total number of interviews to be performed in each semiannual wave will be 900. Follow-up will include a standard instrument (AFA) and HIV testing. Intervention in Oakland will include only HIV testing and counseling in the first year. Intensive ethnographic mapping and qualitative evaluation of interventions will also be conducted throughout the study period. The study is significant because it will: (a) provide HIV surveillance data on out-of-treatment IVDUs consistent with CDC guidelines; (b) evaluate the impact of prevention programs directed toward the IVDU; (c) test the applicability of conceptual frameworks that undergird prevention programs; (d) serve a public health function through the preventive value of routine screening and counseling of IVDUs for HIV-1 infection and their referral to appropriate services and health care; and (D provide an empirical basis for policy and program planning efforts germane to HIV prevention services directed at IVDUs.