The immunologic and virologic activity of nevirapine in combination with two nucleosides (zidovudine [ZDV] and didanosine [ddI]) was evaluated in antiretroviral-naive patients with a CD4 count <200/mm3 or clinical AIDS. In all, 68 patients were enrolled in a 48-week double-blind, placebo-controlled trial. A group of 32 patients received ZDV + ddI + nevirapine, and 36 patients received ZDV + ddI. Primary efficacy parameters were the activity on HIV-1 RNA and on peripheral blood CD4+ cells, with differences between groups analyzed by the Wilcoxon's nonparametric two-sample test. Baseline RNA was high in both treatment groups (median values, 5.8 and 5.7 log10). RNA and CD4 responses were significantly higher with the triple combination (median RNA reductions, 2.69 versus 1.05 log10 at 24 weeks and 1.97 versus 1.20 log10 at 48 weeks; median CD4 increases, 81 versus 64 cells/mm3 at 24 weeks and 101 versus 27 cells/mm3 at 48 weeks). This study demonstrates that a triple combination of ZDV + ddI + nevirapine used as first-line regimen in antiretroviral-naive patients can induce sustained virologic and immunologic response in patients with low CD4 count or a previous diagnosis of AIDS.