The polymerase chain reaction (PCR) as applied to human cytomegalovirus (HCMV) detection should provide a valuable tool for rapid, reliable diagnosis of infection, thereby allowing prompt treatment. However, to date the high sensitivity of this technique and the lack of semi-quantitative interpretation have hindered establishing its validity for diagnosing systemic infection. We describe a rapid, simple, semi-quantitative PCR technique for HCMV detection. The validity of the technique was tested objectively by analyzing over 2000 leukocytes specimens by PCR and comparing the results with virus isolation from urine and blood in concomitant samples in the absence of any clinical data. It could thus be established that this technique had a sensitivity and specificity of 97%. When the PCR signal corresponded to > or = 8000 genome equivalents for 10(4) leukocytes, the predictive value for viremia was 86%. This semi-quantitative PCR technique should allow rapid diagnosis of systemic infection and provide a reliable means of monitoring clearance of CMV from blood during drug therapy.