Mothers are randomized to receive either a single oral dose of NVP during labor or the corresponding NVP placebo. Randomization occurs at any time after the 28th week of gestation. To assure balance between the treatment groups, the randomization is stratified using 2 factors: 1) use of antiretroviral therapy during the current pregnancy (no antiretroviral therapy at all; monotherapy [with no multi-agent therapy] for any duration; multi-agent therapy for any duration), and 2) CD4 cell count at the time of randomization (less than 200 cells; 200 to 399 cells; 400 cells or greater). Mothers are followed on-study for 4 to 6 weeks postpartum.