Controlled studies of the pharmacokinetics and safety of new drugs are critical to the development of alternative therapies for the prevention of perinatal transmission of HIV-1. The dosing regimen of RTV and ZDV used to treat pregnant women in this study has been shown to be safe and effective against HIV in adults. Little is known about the metabolism and tolerance of these drugs during pregnancy, and Phase I studies are needed to determine dosage, safety, and tolerance. Protease inhibitors in combination with other antiretroviral drugs may help reduce the rate of perinatal transmission of HIV-1.