A modified centrifugation culture technique and a polymerase chain reaction (PCR) is described for detection of early antigen and IE antigen DNA, respectively, for rapid and sensitive monitoring of active cytomegalovirus (HCMV) infection after organ transplantation. In a preliminary study, 541 clinical specimens (blood, urine, bronchoalveolar lavage, pharyngeal wash, sputum) from 59 organ recipients were assayed for HCMV antigen by centrifugation culture; 144 samples were tested by PCR simultaneously. Antigenemia detected by centrifugation culture correlated strongly with active HCMV infection and clinical symptoms and proved useful for monitoring the efficacy of anti-viral therapy. PCR was more sensitive in an earlier phase of infection when centrifugation culture was still negative. The clinical usefulness of both methods is discussed.