AMENDED: 9/28/90 Patients are assigned to one of 2 treatments under a double-blind, randomly allocated, experimental design if their duration of prior AZT therapy is 0 to 16 weeks. (Patients who entered with no more than 16 weeks prior AZT and who were randomized to ddI will continue to be dosed at that level, adjusted for weight, and followed as originally planned.) Patients are assigned to one of 3 treatments as explained prior to this amendment if their duration of prior to AZT therapy is greater than 16 weeks. Original design: Patients are assigned to one of three treatments under a double-blind randomly allocated experimental design. ddI will be administered at two dose levels.