Evaluation of Patients Who Have Not Had Success With Zidovudine

Inclusion Criteria Concurrent Medication: Allowed: * Chemoprophylaxis against Pneumocystis carinii pneumonia (PCP), Mycobacterium tuberculosis, or Herpes simplex virus, or against other opportunistic infections as indicated. * Corticosteroids for no longer than 21 days (only as part of PCP therapy). * Erythropoietin and G-CSF. Patients must have: * Documented HIV-seropositivity. * CD4 count 100 - 300 cells/mm3. * Prior continuous AZT dose = or \> 300 mg/day for 1 year or longer. Prior Medication: Required: * AZT for at least 1 year prior to study entry. Exclusion Criteria Co-existing Condition: Patients with the following symptoms and conditions are excluded: * Medical contraindication or is considered noncompliant in the opinion of the investigator. * Peripheral neuropathy = or \> grade 2. Concurrent Medication: Excluded: * Anti-HIV agents other than study drugs. * Biologic response modifiers (other than erythropoietin or G-CSF). * Systemic cytotoxic chemotherapy. * Regularly prescribed medications (such as antipyretics, analgesics, allergy medications) that are associated with an increased risk of pancreatitis, peripheral neuropathy, or bone marrow suppression. Concurrent Treatment: Excluded: * Radiation therapy. Patients with the following prior conditions are excluded: * History of acute or chronic pancreatitis, gout, or uric acid nephropathy. Prior Medication: Excluded: * Other antiretrovirals besides AZT. * ddI or ddC for more than 30 days within the past year or any time within 3 months prior to study entry. * Acute therapy for an infection or other medical illness within 14 days prior to study entry.