In part I, four patients who are now receiving AZT at the usual dose take part in pharmacokinetic studies (how much of the drug enters the blood stream, what happens to the drug in the body, and how it leaves the body) of AZT defined after a dose while at steady state and then again after a new steady state has been reached following the addition of quinine sulfate. Part II studies the pharmacokinetics of AZT in eight patients receiving AZT at 1 of 2 doses and then at the lower dose of AZT plus probenecid with or without quinine.