The capsules contain either AZT or placebo and are identical in appearance so that neither patient nor physician knows which treatment the patient is receiving. The higher dose corresponds to the dose found to be useful in patients with AIDS or severe ARC. Patients visit the clinic every 2 weeks for the first 16 weeks, then once a month after that for evaluation. Treatment will continue until the results from the study have been analyzed, which could be as long as 3 years. If side effects occur, the dose of study medication will be decreased or temporarily stopped. If the side effects are severe, then study medication will be stopped permanently.