In this 6-month prospective study, we compared the efficacy of two treatment regimens: double-drug therapy with zidovudine (ZDV) and lamivudine (3TC) and triple-drug therapy with ZDV plus 3TC plus nelfinavir (NFV), in the treatment of asymptomatic and early symptomatic HIV-infected children. Twenty-five children were enrolled in this study and were divided into 2 groups: group A, consisting of 13 children who were given ZDV+3TC; group B, consisting of 12 children who were given ZDV+3TC+NFV. Serial determinations of weight, CD4-cell count, HIV RNA or plasma viral load (VL) and complete blood counts (CBC), liver function tests (LFT), blood urea nitrogen (BUN) tests, creatinine and serum amylase tests were performed at study entry and at 1, 3 and 6 months. The side-effects of drugs were recorded. Over the 6-month period, the median weight increase in group B (24%) was higher than in group A (2%). The median CD4-cell count increase from baseline in group B (94.5%) was better than in group A (9.4%). The reduction of VL below baseline in group B (1.2 log10; 20.8%) was also better than in group A (0.72 log10; 13.8%). However, these differences were not statistically significant (p>0.05). Both combination regimens could not completely suppress HIV RNA below detectable limits (<400 copies/ml). Both groups tolerated the regimens well; no side-effects or toxicities occurred. The efficacy levels of triple-drug therapy (ZDV+3TC+NFV) and double-drug therapy (ZDV+3TC) were not different. There were no side-effects and no deaths during the 6-month study period.