Eligible women who elect to participate in this study will be enrolled in either the Late Presenter Group (women who are not in active labor, and for whom delivery is not imminent) or the Peripartum Group (women who are in active labor with anticipation of delivery within 24 hours). Step I for all women will include rapid HIV testing with OraQuick HIV 1/2 and standard testing with enzyme-linked immunosorbant assay (EIA) or Western blot. Women with a positive HIV test and their infants will be offered preventative antiretroviral therapy and enrollment into Step II. Step II will include clinical evaluations, laboratory evaluations, and an adherence assessment for the women and their infants. Women in the Late Presenter Group who participate in Step II will have one prenatal visit, a visit at labor and delivery, and three postpartum visits. Women in the Peripartum Group who participate in Step II will have three postpartum visits. All infants in Step II will have five study visits through 24 weeks of age.