Over 90% of HIV infection in children results from perinatal transmission; the most important goal of the Pediatric ACTG is to determine which approach will prevent and/or decrease HIV transmission. Antiretroviral agents as well as passive and active immunization will be utilized alone and in combination to after transmission of HIV from mother to child. The impact of antiretroviral therapy on HIV infected children will be determined as new agents become available; combination therapy, utilizing drugs that inhibit HIV replication at different phases of its life cycle, will be evaluated during the next four years. As HIV infected children survive longer, opportunistic infections will become more prominent and effective prophylaxis and therapy will be defined. The Northern California Pediatric AIDS Treatment Center is a consortium of tour subunits dedicated to the provision of treatment protocols to HIV infected pregnant women, children, and adolescents living in a 12 county area and representative of the ethnic diversity of the region. The University of California, San Francisco (UCSF) serves the North Bay, Childrens' Hospital Oakland (CHO) the East Bay, and Stanford University (SU) the South Bay. The Bay Area Perinatal AIDS Center, the referral facility for HIV infected pregnant women throughout Northern California, is at the fourth subunit, San Francisco General Hospital (SFGH). The adolescent component of the UCSF subunit is located in the community and identifies HIV infected disenfranchised youth. During the upcoming year, the four subunits propose continuing 80 patients on treatment trials and enrolling 53 new patients to ACTG protocols; of the 53 patients enrolled to new trials during Year 01, 42 will be patients never before enrolled in an ACTG protocol. Vaccine trials will be emphasized in HIV infected pregnant women to after transmission, in infants born to these women to decrease transmission, and in infected infants to alter disease progression. CHO and SU will participate primarily in antiretroviral trials; CHO and UCSF will participate in trials of prophylaxis for opportunistic infections. Investigators at all four subunits are active participants in the ACTG. UCSF investigators provide ACTG scientific leadership with expertise in immunology and a focus on the vaccine scientific agenda. Investigators at all subunits will submit concept sheets and serve as protocol chairs to advance the clinical investigation of the ACTG. The Immunology and Virology Core Laboratories will provide assays in support of ACTG protocols; both laboratories will continue to refine assays in order to support new clinical investigation initiatives. The Immunology Core Laboratory will act as a National Center to provide assays of surrogate markers as well as IgA anti-HIV for national trials.