AMENDED: 8/29/90 Inclusion of asymptomatic patients with CD4 counts less than 200 cells/mm3. Standardization of baseline evaluation schedule to allow 14 days prior to study dosing. Reduction in frequency and intensity of follow-up evaluations. Standardization of study endpoints. Inclusion of toxicity scoring and management for amylase and triglyceride elevations. Clarification of concomitant medication use. Original design: To determine the effectiveness of didanosine (ddI) in patients with AIDS or advanced AIDS related complex (ARC) who have documented hematologic intolerance to zidovudine (AZT) therapy. To determine if the efficacy of ddI increases with increasing doses.