Mothers in the AZT group receive either a bolus of AZT or its placebo at onset of labor, then doses every 3 hours until delivery, with follow-up to 6 to 8 weeks. Infants begin receiving either a lower dose of AZT or placebo as soon as they can tolerate liquids by mouth, twice daily for 7 days, and are followed for 18 months as in the NVP group.