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.