AMENDED: The trial will proceed as described above except that the first 2 methadone patients enrolled will receive half the AZT dose given to the non-methadone patients. Results will be evaluated before dosing of additional methadone-use patients is done. Original design: Following evaluation, patients receive one intravenous dose of AZT over a 1-hour period. One day later, patients begin taking AZT capsules 5 times a day by mouth for the remaining weeks prior to labor.