A Comparative Study of a Combination of Zidovudine, Didanosine, and Double-Blinded Nevirapine Versus a Combination of Zidovudine and Didanosine

Inclusion Criteria Concurrent Medication: Required: * PCP prophylaxis for patients with CD4 count \< 200 cells/mm3 or a prior history of PCP. Allowed: * Trimethoprim with sulfamethoxazole or dapsone, intravenous pentamidine, atovaquone, primaquine-clindamycin or trimetrexate for acute PCP. * Topical antifungals, clotrimazole, ketoconazole, fluconazole, and amphotericin B for treatment of mucosal and esophageal candidiasis. * Prophylaxis or therapy for opportunistic infections, as indicated, with other medications such as itraconazole, isoniazid, pyrazinamide, clofazimine, clarithromycin, azithromycin, ethambutol, amikacin, ciprofloxacin, ofloxacin, pyrimethamine, sulfadiazine, and clindamycin. * Maintenance therapy for opportunistic infections as long as patients have been on a stable dosage regimen for 1 month prior to study entry. * Ganciclovir for CMV retinitis or gastrointestinal disease as long as patients have been on a stable dose for at least 1 month prior to study entry with no grade 3 or 4 neutropenia or dependence on G-CSF. * Acyclovir (\<= 1000 mg/day) for maintenance of herpes simplex virus infections. * Erythropoietin or G-CSF if clinically indicated. * Antibiotics for bacterial infections unless specifically excluded. * Rifampin or rifabutin. * Symptomatic treatments such as antipyretics, analgesics, and antiemetics. Concurrent Treatment: Allowed: * Local radiation therapy. Prior Medication: Required: * At least 6 months of prior cumulative nucleoside therapy with AZT, ddI, or ddC, given as monotherapy or in combination. Patients must have: * Prior or current documentation of HIV seropositivity by ELISA confirmed by Western blot, positive HIV antigen, or positive HIV culture, or a second antibody test by a method other than ELISA. * CD4 count \<= 350 cells/mm3. * Prior cumulative nucleoside therapy of \>= 6 months. * Consent of parent or guardian if less than 18 years of age. Exclusion Criteria Concurrent Medication: Excluded: * Antiretroviral therapies other than study medications. * Systemic corticosteroids given consecutively for \> 21 days. * Induction or maintenance with foscarnet. * Systemic cytotoxic chemotherapy for a malignancy. * Erythromycin. * Coumadin/warfarin. * Phenytoin or phenobarbital. * Amoxicillin/clavulanate acid (Augmentin) or ticarcillin/clavulanate acid (Timentin). Patients with the following prior conditions are excluded: * History of pancreatitis. * History of intolerance to 500 or 600 mg/day AZT or to 400 mg/day ddI tablets or 500 mg/day ddI sachets. * History of grade 2 or worse peripheral neuropathy. Prior Medication: Excluded at any time: Prior non-nucleoside reverse transcriptase inhibitors (NVP; L697,611; TIBO; atevirdine). Excluded within 14 days prior to study entry: * Acute treatment for a serious infection or any opportunistic infection. * Biologic response modifiers such as interferon and IL-2. * Erythromycin. * Coumadin/warfarin. * Phenytoin or phenobarbital. * Ticarcillin/clavulanate acid (Timentin) or amoxicillin/clavulanate acid (Augmentin).