In HIV-infected patients, the presence of cytomegalovirus (CMV) viraemia is predictive of the development of acquired immunodeficiency syndrome (AIDS), but it is not known whether it predicts further occurrence of CMV organ involvement. To assess the predictive value of CMV viraemia in the occurrence of CMV organ involvement, CMV blood cultures were performed at the onset of AIDS in 71 patients. They were prospectively followed up for at least 6 months, with a mean of 16.6 +/- 7 months (6-36 months). CMV viraemia was present in 28/71 patients (39.5%) at the onset of AIDS. CMV organ involvement occurred in 18/71 patients (25.4%) after 8.7 +/- 3.3 months. Fourteen of the 28 patients (50%) with early CMV viraemia developed CMV organ involvement after 7.7 +/- 6.3 months as compared with 4/43 patients (9.3%) who were not viraemic at the onset of AIDS with a mean follow-up of 11.8 +/- 3.8 months (P less than 0.001). At the time of CMV organ involvement, CMV viraemia, however, was present in 94.4% of the cases. No differences in survival was observed between initially viraemic and non-viraemic patients. No difference has found in mean CD4 cell count between viraemic and non-viraemic patients. This high predictive value of early CMV viraemia in AIDS for the occurrence of CMV organ involvement underlines the need for repeated search for CMV organ involvement when CMV viraemia is detected, and for less toxic antiviral drugs that might be used earlier.