A randomized, double-blind, multicenter study of indinavir, zidovudine, and lamivudine was conducted in 320 adults with human immunodeficiency virus type 1 (HIV-1) infection, </=50 CD4 cells/mm3, and extensive prior zidovudine therapy. Patients received indinavir, 800 mg every 8 h; zidovudine, 200 mg every 8 h, and lamivudine, 150 mg twice daily; or all 3 drugs for 24 weeks. In an intention-to-treat analysis, proportions of patients with HIV-1 RNA <500 and <50 copies/mL, respectively, at week 24 were 56% and 45% in the indinavir-zidovudine-lamivudine group, 3% and 2% in the indinavir group, and 0% in the zidovudine-lamivudine group. Observed mean CD4 cell increases were 95, 78, and 6 cells/mm3 in the three-, one-, and two-drug arms, respectively. Regimens were generally well tolerated. Patients with advanced HIV-1 infection benefit from triple therapy with indinavir, zidovudine, and lamivudine, although the proportion with optimal response appeared to be lower in patients with low CD4 cell counts.