To assess the effect of highly active antiretroviral therapy (HAART) on cytomegalovirus (CMV) antigenaemia in AIDS patients, 70 patients with CD4+ cell counts < or = 50/mm3 and positive anti-(CMV) immunoglobulin G (IgG) were tested at 15-30 day intervals for CMV antigenaemia. We selected those patients who had been followed up for more than 3 months. Three patient profiles were defined: A, followed up before the introduction of HAART; B, followed up before and after the use of HAART; and C, followed up after the use of HAART. Thirty-nine patients were included, 12 in group A, 17 in group B, and 10 in group C. Group A patients presented a lower median CD4+ cell count compared with groups B and C patients (9, 122 and 127 cells/mm3, respectively), with the increase in the last 2 groups being related to the use of HAART (P<0.001). A lower proportion of positive antigenaemia was observed in group B after the introduction of HAART compared with the time before HAART (P=0.02). HAART caused an immunological improvement and was found to be associated with negativity of CMV antigenaemia.