Brazil is a mid-developed country with one of the highest seroprevalence rates of HIV in Latin America and an increasing number of new cases in women. We at UCLA have established a new consortium of collaborators between investigators in Brazil and in the US for studies of HIV-1 transmission. We propose to participate in the scientific agenda of the HPTN as a clinical unit for international studies in Brazil for prevention of HIV perinatal and heterosexual transmission. Brazil is a unique site for performance of clinical trials because it has advanced infra structure and issues relevant to both industrialized and developing nations. We plan to conduct phase I, II, and III clinical trials addressing important issues of HIV perinatal transmission which will be based on important questions of HIV pathogenesis. Results of these studies will be applicable to Brazil, and to both industrialized and developing countries. Because of the rising incidence of HIV infection particularly in women, Brazil is highly suitable for studies of prevention of sexual transmission in HIV uninfected high- risk populations, especially through trials of treatment of sexually transmitted diseases, use of microbicides and behavioral approaches. We have established a collaboration with outstanding investigators from three sites in Brazil where populations of HW infected mothers and exposed infants and HIV negative high risk women are available for recruitment into perinatal and intervention trials. We have the capability to expand prevention trials not only to other sites within Brazil, but to additional populations similarly affected by HIV, such as adolescents (including street youth), intravenous drug users, commercial sex workers or men who have sex with men. Our laboratory facilities at UCLA and research experience, combined with outstanding research facilities and human resources at our core laboratory site in Brazil, can generate high quality immunology and virology laboratory capabilities to provide both standard and innovative assays to support the clinical trials and the HPTN scientific agenda.