Three studies are planned on two separate patient groups. Group (1) Patients who have never taken AZT start on a standard dose of AZT. Blood samples are taken hourly for an 8-hour period on days 1 and 14. Other blood samples are taken on days 2, 4, and 8. Group (2) Patients who have never taken AZT are given a standard dose for the first week, increasing each week until week 5. Blood samples are taken at the end of each weekly treatment. After 4 weeks of standard treatment, patients in groups 1 and 2 return and receive a single morning dose of oral AZT. Blood samples are taken immediately before dosing and at 1, 2, 4, 6, and 8 hours after dosing. After a 48-hour clearance period, patients return and resume dosing. Blood samples are again taken over an 8-hour period. After 24 weeks of standard treatment, the pharmacokinetic studies are repeated.