Persons with severe mental illness are at disproportionate risk for exposure to HIV. Substance use including many non-injection related behaviors, are associated with transmission risk. Research with other populations has demonstrated that reductions or changes in substance use can significantly impact sexual risk behaviors, suggesting that substance use should be a primary target of HIV prevention efforts. To date, there is a dearth of research investigating the impact on sexual risk behaviors on interventions targeting the substance use practices of persons with severe mental illness who also have substance use disorders. This project therefore proposes to conduct a Stage lb behavioral intervention trial (Rounsaville et al., 2001) targeting sexual risk reduction for persons with dual diagnosis (severe mental illness and substance use disorder). This project will be conducted in two phases. Phase one will be devoted to developmental work using focus groups to explore intervention content and developing procedures for recruiting, engaging, and retaining participants in longitudinal research that involves attending multiple intervention sessions. We will also develop and pilot test two new measures, one assessing incremental changes in substance use and another assessing peer support for HIV preventive behaviors. In phase two we will evaluate the intervention programs randomly assigning 120 eligible participants, equal numbers of men and women, to one of three conditions: 1) wait-list control + cognitive-behavioral sexual risk reduction (CB); 2) CB + Health Education (HE); or 3) CB + substance use harm reduction (HR). Outcome data will be collected from all participants at immediate post-intervention and 24 weeks after study entry. Key outcomes will include risky sex (e.g., number of occurrences of unprotected intercourse by partner type and number of sexual partners). We will also collect data on a number of substance-using variables (substance use, sexual activity in conjunction with alcohol or drug use, and incremental change) as mediators of change in sexual risk. It is anticipated that this work will lead to the development of a proposal for a full-scale efficacy' study.