A Double-Blinded, Randomized Trial Comparing Zidovudine (AZT) Versus AZT Plus Didanosine (ddI) Versus AZT Plus ddI Plus Nevirapine in Asymptomatic Patients on AZT Monotherapy Who Develop a Mutation at Codon 215 of HIV Reverse Transcriptase in Serum/Plasma Viral RNA

Inclusion Criteria Concurrent Medication: Allowed: * Chemoprophylaxis for Pneumocystis carinii pneumonia. * Antibiotics, antifungals, and antiviral medications, as clinically indicated. * Regularly prescribed medication such as antipyretics, analgesics, allergy medications, antidepressants, sleep medications, oral contraceptives, or any other medications deemed appropriate by the primary care provider. Concurrent Treatment: Allowed: * Limited localized radiation therapy to the skin. Prior Medication: Required: * AZT (minimum 300 mg/day) for at least 1 month (uninterrupted) but no more than 2 years immediately prior to study entry. Patients must have: * Asymptomatic HIV infection. * CD4 count 300-600 cells/mm3. * No plasma/serum PCR for codon 215 mutation at screening. * Prior AZT monotherapy. NOTE: * All Department of Defense (DOD)-eligible patients must be at least 18 years of age. Enrollment of women is encouraged. AS PER AMENDMENT 04/03/95: * DOD female patients must have a negative pregnancy test within 48 hours prior to study entry. Exclusion Criteria Co-existing Condition: Patients with the following symptoms or conditions are excluded: * Symptomatic grade 2 or worse peripheral neuropathy. * Unable to swallow capsules and tablets. * Other medical condition that contraindicates study participation. Concurrent Medication: Excluded: * Systemic cytotoxic chemotherapy. * Biologic response modifiers (such as interferon, ampligen, or PEG-IL2). * Anti-HIV agents other than study drugs. * Other investigational agents. * Foscarnet unless clinically indicated for unresponsive herpes virus infection. * Chronic antacid or H-2 blocker use. * Rifampin or rifamycin class agents. * Antibiotics containing clavulanic acid. Concurrent Treatment: Excluded: * Radiation therapy other than limited localized therapy to skin. Patients with the following prior condition are excluded: * History of pancreatitis. Prior Medication: Excluded: * Prior therapy with nucleoside or non-nucleoside antiretroviral agents other than AZT. * Immune modulating therapies (e.g., IFN-alpha, gp160) within 60 days prior to screening. Prior Treatment: Excluded: * Blood transfusion within the preceding 2 weeks. Illicit drug or alcohol abuse.