 Women will be enrolled between 28 and 38 weeks of gestation. As part of normal PMTCT services, they may choose NVP-boosted ZDV or single dose NVP for PMTCT; We anticipate that most 80 will choose the former. At arrival for delivery, they will be randomized to receive either the two study drugs intervention or no drug control. A total of 400 women will be randomized, and followed, along with their infants, for 6 months. 