The presence of human cytomegalovirus (HCMV) DNA in blood was investigated by the polymerase chain reaction (PCR) in 293 blood samples from 86 immunocompromised patients. Of the 86 patients, 23 underwent clinical and virologic follow-up for HCMV infection. In parallel, blood samples were examined for viremia and antigenemia. Concordant results between PCR and assays for viremia and antigenemia were obtained on 124 positive and 110 negative samples, with an overall concordance of 79.8%, while 59 samples (most from patients with HCMV infection) were positive by PCR alone. PCR is a new powerful tool for detection of HCMV infections in blood samples from immunocompromised patients. However, its clinical significance appears to be restricted to the indication of a risk of reactivation of HCMV infection.