A Multi-Center, Placebo-Controlled, Double-Blind, Randomized Trial Comparing the Virologic and Immunologic Activities of 400 Mg Nevirapine in Combination With Zidovudine Versus Zidovudine Alone in Asymptomatic HIV-1 Infected Patients With 4-12 Months of Prior Zidovudine Therapy and 200-500 CD4+ Cell

Inclusion Criteria Concurrent Medication: Allowed: * PCP prophylaxis (trimethoprim-sulfamethoxazole, dapsone, or aerosolized pentamidine), at the discretion of the investigator. * Antifungal prophylaxis with oral fluconazole or ketoconazole. * Antiviral prophylaxis for herpes simplex virus with \<= 1000 mg/day oral acyclovir. * Dilantin for prevention and treatment of seizures. Patients must have: * Asymptomatic HIV infection. * CD4 count 200-500 cells/mm3. * No prior AIDS. * No history of or active HIV-related thrush, vaginal candidiasis, zoster (shingles), excessive weight loss, persistent fever, or diarrhea. * Tolerated 500-600 mg AZT daily for at least 4 months but no more than 12 months immediately prior to study entry. * Consent of parent or guardian if less than 18 years of age. NOTE: * Patients may not co-enroll in another protocol involving other investigational drugs or biologics. Exclusion Criteria Co-existing Condition: Patients with the following symptoms or conditions are excluded: * Malignancy other than limited cutaneous basal cell carcinoma. * Psychiatric condition sufficient to impair study compliance. Concurrent Medication: Excluded: * Systemic glucocorticoids and steroid hormones. * Dicumarol, warfarin, and other anticoagulant medications. * Cimetidine. * Tolbutamide. * Doxycycline. * Chloramphenicol. * Phenobarbital and other barbiturates. * Foscarnet. * Erythromycin. * Amoxicillin-clavulanate (Augmentin). * Ticarcillin clavulanate. * Biologic response modifiers (alpha interferon, IL-2, immune modulators). * Any investigational drugs other than study drugs. Patients with the following prior condition are excluded: History of clinically important disease other than HIV infection, that may put patient at risk because of participation in this study. Prior Medication: Excluded: * Antiretroviral medications other than AZT. Excluded within 4 weeks prior to study entry: * Immunosuppressive or cytotoxic drugs or other experimental drugs. * Systemic glucocorticoids and steroid hormones. * Dicumarol, warfarin, and other anticoagulant medications. * Cimetidine. * Tolbutamide. * Doxycycline. * Chloramphenicol. * Phenobarbital and other barbiturates. * Foscarnet. * Erythromycin. * Amoxicillin-clavulanate (augmentin). * Ticarcillin clavulanate. * Biologic response modifiers (alpha interferon, IL-2, immune modulators). Required: * AZT at 500-600 mg/day for at least 4 months but no more than 12 months immediately preceding study entry. Chronic use of alcohol or drugs sufficient to impair study compliance.