AMENDED: For the pharmacokinetic and safety study of AZT during labor and in the newborn infants, women who were screened and have consented are included in this part of the study. 6 mother-infant pairs without a history of intravenous drug abuse and 4 pairs with such a history are evaluated. The mother receives an infusion of AZT over 1 hour followed by continuous infusion of AZT for at least 4 hours until delivery. Pharmacokinetic data is collected on all patients including those who deliver before receiving 4 hours of AZT infusion.