This study will identify cellular and humoral immune factors which correlate with vertical transmission of HIV infection and will investigate in vitro correlates of passive immunization. First, cellular and humoral immunity will be measured in the mother during pregnancy. Evaluations will include gp120-specific T lymphocyte (CTL) and cell-mediated (CMC) cytotoxicity, proliferative and interleukin-2 (IL-2) production in response to intact gp120 and defined gp120 peptides, neutralizing activity of maternal serum and monoclonal antibodies against maternal and diverse laboratory strains of HIV-1, and the ability of maternal serum to arm normal and infant effector cells. Second, cellular and passively-acquired humoral immunity will be evaluated in the infant at birth, by measuring CTL and CMC responses, proliferation and IL-2 production, neutralizing activity and the ability of infant sera to arm normal lymphocytes. Third, cellular and humoral immunity in the infant at 8 weeks and 6 months of age will be evaluated by measuring gp120-specific CTL and CMC activity, proliferation and IL-2 production, and neutralizing activity. Results from these in vitro assays of humoral and cellular immunity will be correlated with evidence of infection in the child. If it can be determined which aspects of immunity are important in preventing vertical transmission, then an attempt can be made to enhance specific immunity in those mothers who are likely to transmit HIV infection to their infants.