This research proposes to enhance an ongoing innovative day treatment program for substance abusing homeless persons, including work and housing interventions, with new state-of-the-art treatment for cocaine dependance. Results from a NIAAA/NIDA research demonstration in 1991 revealed that day treatment was significantly more effective than usual care in establishing abstinence, improving independent housing, and increasing days employed and earned income. Findings also showed that 77% of the clients were cocaine abusers or cocaine dependent and most had associated DSM III-R mental disorders. This research proposes to target treatment more precisely to the population found in the 1991 demonstration and to extend the most effective treatment for initiating cocaine abstinence from recent research to a more dysfunctional dually diagnosed homeless population. This study is also designed to address the question: What are the sufficient conditions for effective treatment of homeless substance abusers? Is effective treatment for Substance Use Disorders sufficient to produce improvement in, not only substance abuse, but homelessness and unemployment? The proposal establishes a new cohort of 150 cocaine abusing homeless persons with a co-existing non-psychotic mental illness. It will compare a behavioral social reinforcement day treatment program for cocaine abuse, plus abstinence contingent housing and work therapy vs. a day treatment control, which does not include abstinence contingent housing and work therapy, on initiating abstinence and reducing homelessness and unemployment. This study will yield important information on the necessary and sufficient conditions needed for effective treatment of homeless persons with Substance Use Disorders. The proposed study takes a first step in separating interventions for homelessness vs. substance abuse, and discovering if these combined interventions are necessary and sufficient or, if effective intervention for substance abuse is sufficient alone for treatment of substance abusing homeless. Thus, information from this study will provide important knowledge on how to most effectively treat this difficult population, knowledge which has important clinical, economic and public policy implications.