Senegal is a West African country with significant rates of both HIV-2 and HIV-1 infection. In sub-Saharan Africa, sexually active women of child- bearing age are considered at risk for both HIV-1 and HIV-2. There is a tremendous need to better understand perinatal transmission and its potential effect on pediatric populations. Currently, there is little data available on perinatal transmission and the natural history of perinatally acquired HIV-2 infection. Our proposed studies hope to provide more information on HIV-1 and HIV-2 perinatal transmission and disease development. This will provide important data needed to devise health strategies for the prevention of HIV infection. A. SPECIFIC AIMS: (1) To determine the risk factors an rate of perinatal transmission for both HIV-2 and HIV-1. (2) To determine if mother and infant antibody responses to various HIV antigens or epitopes may be useful in distinguishing passive from active antibodies in infants (<18 months old). These antibody markers will also be assessed as prognostic markers for HIV pathogenesis. (3) To determine the utility of PCR in the early diagnosis and sequential assessment of active HIV-1 or HIV-2 infection in infants. (4) To determine the clinico-immunologic abnormalities that occur in the natural history of perinatally acquired HIV-1 and HIV-2 infection. (5) To study the morbidity/mortality experience in HIV exposed versus nonexposed infants.