BACKGROUND: The optimal neonatal antiretroviral (ARV) regimen for prevention of HIV mother-to-child transmission (MTCT) is unknown for infants born to mothers who receive no ARVs during pregnancy. METHODS: As part of a protocol comparing the efficacy of 3 neonatal ARV regimens in preventing HIV-1 MTCT in neonates born to mothers who receive no prenatal treatment with ARVs, we devised a 3-dose nevirapine (NVP) regimen with the goal of maintaining the NVP plasma concentration >100 ng/mL (10 times the in vitro median inhibitory concentration of 10 ng/mL) during the first 2 weeks of life. NVP concentrations were measured in 14 newborns participating in a pharmacokinetics substudy during the second week of life and in single samples from 30 more newborns on day 10 to 14. RESULTS: The median NVP elimination half-life was 30.2 hours (range: 17.8 to 50.3 hours). The NVP concentration remained greater than the target of 100 ng/mL in all samples collected through day 10 of life. By day 14, more than half of the newborns in the pharmacokinetic substudy had NVP levels <100 ng/mL, although only 1 neonate had no detectable NVP. CONCLUSION: Although this regimen failed to meet our 100-ng/mL target, it did maintain detectable NVP concentrations in nearly all newborns through the end of the second week of life and is to be used in the parent efficacy protocol.