Patients are placed by random selection into one of three groups to receive either AZT alone, ddI alone, or AZT and ddI. This is a double-blind study: neither patient nor treating physician knows which group patient is in. If patients are receiving either AZT or ddI alone and they develop drug toxicity (after dose reduction), or if HIV disease progresses, the alternative single drug is offered. If patients receiving both drugs develop drug toxicity (despite dose reduction) or if HIV disease progresses, they discontinue study drug and are offered the best alternative therapy. PER AMENDMENT 6/26/95: Initial monotherapy AZT arm is unblinded and no further crossover therapy for any arm is permitted. Patients who reach crossover criteria on initial blinded ddI or AZT+ddI will be unblinded and permanently discontinued from study drugs.