Women are randomized to receive either NVP or the corresponding placebo in active labor. Women are randomized at any time after their 32nd week gestation [AS PER AMENDMENT 1/13/98: 28th week gestation] [AS PER AMENDMENT 2/23/00: 20th week gestation]. The randomization is stratified using two factors: (1) use of [AS PER AMENDMENT 2/23/00: current or anticipated] antiretroviral therapy during the current pregnancy (no therapy at all; monotherapy for any duration; multi-agent therapy for any duration), and (2) CD4 cell count at the time of randomization (less than 200 cells; 200 - 399 cells; 400 cells or greater). Mothers are followed on study for 4 to 6 weeks postpartum. Mothers are also encouraged to follow the regimen of zidovudine (ZDV) outlined in the Office of Public Health and Science (PHS) treatment guidelines for both themselves and their infants. Infants are administered either NVP or placebo between 48 and 72 hours of life. The infant's study drug is the same as the mother's randomized treatment assignment. Infants are dosed with the study drug according to their randomization group regardless of whether the mother received the study drug. Infants are followed for 4 to 6 weeks, and are tested for HIV at 4 to 6 weeks, 3 months, and 6 months.