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

PRIMARY: To compare the virologic activity (quantitative RNA PCR, quantitative PBMC) of the combination of nevirapine and zidovudine (AZT) versus AZT alone after 3 and 6 months of treatment. To compare the effects of these two regimens on CD4 T-cell count and percentage. SECONDARY: To compare and evaluate other markers of immunologic and virologic activity in patients receiving nevirapine/AZT versus AZT alone. To compare the effects of the two regimens on clinical signs and symptoms. To evaluate the safety and tolerance of the two regimens.