From July 1, 1999 to April 30, 2002, 111 consecutive human immunodeficiency virus-infected, antiretroviral-naïve Taiwan patients initiated highly active antiretroviral therapy with efavirenz plus 2 nucleoside reverse-transcriptase inhibitors. Their median baseline CD4+ count was 50 x 10(6)/L (0-559 x 10(6)/L) and plasma viral load was 5.51 log10 copies/mL (3.09 to > 5.88 log10) as assessed by reverse-transcriptase polymerase chain reaction. Of the patients, 52.3% had a CD4+ count of < or = 50 x 10(6)/L, 74.8% had plasma viral load over 5 log10 copies/mL, and 58.5% had active AIDS-defining opportunistic illnesses. The median observation duration of antiretroviral therapy was 350 days (range, 28-991 days). At week 48 to 52 following the initiation of highly active antiretroviral therapy, 81. 8% (45/55) and 91.8% (45/49) of the patients achieved undetectable plasma viral load by intent-to-treat and ontreat analysis, respectively. At week 80 to 84, these percentage decreased to 69.7% (23/33) and 85.2% (23/27), respectively. Median CD4+ count increased from baseline to week 48 to 52 by 147 x 10(6)/L and to week 80 to 84 by 227 x 10(6)/L. The virologic and immunologic responses at each time period by intention-to-treat or on-treat analysis were similar between patients with baseline plasma viral load over or < or = 5 log10, CD4+ count over or < or = 50 x 10(6)/L, and with or without active AIDS-defining opportunistic illnesses. After initiation of highly active antiretroviral therapy for a median duration of 57 days (range, 2-638 days), 11 episodes of AIDS-defining and 11 non-AIDS opportunistic illnesses occurred. The results of this study suggest that efavirenz plus 2 nucleoside reverse-transcriptase inhibitors is a potent antiretroviral combination regardless of whether the patient has a high baseline plasma viral load, low CD4+ count, or AIDS-defining opportunistic illnesses.