Patients, who may participate in all three parts of the study, are maintained on a stable dose of AZT. In part A (optimal dose), five AIDS patients who have had an AIDS related opportunistic infection receive 4 once-weekly increasing doses of IFN-G. Monocyte antimicrobial activity is examined in test tube studies before and after each injection of IFN-G. In part B, five patients receive the optimal dose of IFN-G established in part A. Patients enrolled from part A have completed at least 2 weeks of part A before enrolling in part B. Antimicrobial activity is examined 1, 2, and 3 days after a single injection of the optimal dose of IFN-G (determined in part A). In part C (safety and tolerance of combined treatment of IFN-G and AZT), patients are treated with IFN-G for 4 weeks using the optimal dose and administration schedule derived from parts A and B.