OBJECTIVE To assess human immunodeficiency virus (HIV) ribonucleic acid load in children and adolescents with HIV infection who are being treated with antiretroviral combination therapy. METHODS Five patients whose disease progressed with their prior antiretroviral therapy had treatment regimens changed to zidovudine (ZDV)/didanosine (DDI) (group A), and the regimens of six patients were changed to ZDV/lamivudine (3TC) (group B). Patients were followed every 4 to 8 weeks for an average period of 8.6 months. Serial determinations of viral copy numbers and CD4 cells were performed. RESULTS In group A patients' mean relative changes in CD4 cells showed a 20% increase after 4 months (difference not significant (NS)) and a return to baseline after 8 months; in group B patients' mean relative increases of CD4 cells were 72% (p = 0.046) and 50% (NS), respectively. In group A mean relative viral load increased 21% (0.08 log10, NS) and 71% (0.23(10) log, NS), whereas in group B viral load decreased 22% (0.1 log10, NS) and 74% (0.58 log10, p = 0.03) after 4 and 8 months, respectively. After starting antiretroviral combination therapy in group A, there was a slight trend of a decreasing ratio of viral load per number of CD4 cells, whereas in group B this ratio significantly decreased, indicating a marked suppression of viral turnover with ZDV/3TC treatment. CONCLUSIONS In a small cohort of pediatric patients, combination therapy with ZDV/3TC was well tolerated and had a strong and sustained effect on the decrease of viral loads similar to results obtained in adults. In patients with ZDV/DDI therapy the reduction of viral load was less pronounced, but treatment groups A and B were not comparable for statistic evaluation.