Viral load and drug levels were measured in the plasma and breast milk of nine mothers treated with highly active antiretroviral therapy (HAART) and one woman treated only with zidovudine during delivery. In all HAART-treated women after delivery the viral load was less than 400 copies/ml in plasma and breast milk. Compared with the plasma concentration, the breast milk concentration was between 68 and 90% for nevirapine, 6 and 24% for nelfinavir and 90 and 540% for indinavir.