The relationship between cytomegalovirus (CMV) DNA in leucocytes and CMV disease in AIDS patients was sought. In 195 HIV-1 infected, mostly AIDS patients, CMV nPCR was performed in 477 peripheral EDTA blood samples which were collected also for CD4 cell counts (403), classic (410) and rapid virus isolation (270), and antigenemia tests (190). Most patients who died were autopsied. Immunohistopathology for CMV was performed. The first 43 patients were classified clinically according to having (A) verified organ involvement of CMV (15), (B) suspected CMV disease due to symptoms (4), or no CMV-associated disease (24). CMV-DNA was detected in the majority of samples (66%) and patients (68%). In contrast, CMV in the samples was detected in only 16% by classical and 11% by rapid isolation and in 8.4% by the antigenemia test. Acquisition of CMV DNA in leucocytes became more common as the CD4 cell counts fell. Detection of CMV DNA was significantly associated with CMV-associated symptoms and later mortality. In conclusion, CMV PCR of DNA in leucocytes is a sensitive and early marker of CMV disease in HIV-infected AIDS patients. It might be a marker to be added to CD4 cell counts for initiation of preemptive therapy.