Study A: Patients selected for the study are randomly assigned to placebo (inactive medication) or ZDV taken every 4 hours while the patient is awake for a total of 5 doses per day. The patient's immune function and clinical condition are monitored with periodic virus cultures, p24 antigen assays, estimates of lymphocyte type and numbers, cell surface markers, and frequent clinical evaluations to see if these are markers of drug efficacy. Patients continue on their regimen until the final analysis of the data, which could occur up to 3 years after the last patient is entered into the study. Amendment: Based on data from ACTG 019 this protocol has been closed to further accrual. All patients entered in this study will be unblinded as to treatment received. Patients will be informed of results of ACTG 019 and be requested to sign a modified statement of consent approved by the local Institutional Review Board. All patients currently receiving study therapy will be offered open-label ZDV. Patients temporarily discontinued from study therapy at this time will be offered open-label ZDV when toxicity resolves (less than or equal to Grade 2 hemoglobin or neutrophil toxicity, less than or equal to Grade 1 all other toxicities). Patients who have been permanently discontinued from study therapy will not be eligible for open-label ZDV through this protocol. Modification of dose is recommended, however, patients who elect to continue current dose of ZDV after being informed of results of ACTG 019 will be allowed to do so. All patients enrolled in this study will continue to be followed until termination of this study. Above amendment added 11/01/89.