Seventy-five organ transplant recipients underwent prolonged virological and serological follow-up for early detection of human cytomegalovirus (HCMV) infection after transplantation. HCMV DNA detection by nested polymerase chain reaction (PCR) and HCMV early structural antigen (pp65) detection were carried out in 576 peripheral blood leucocyte (PBL) samples. Furthermore, 563 blood specimens were investigated by a commercially available enzyme-linked immunosorbent assay (ELISA) for the detection of specific immunoglobulins G, M, and A against HCMV structural antigens. In eight of nine symptomatic organ transplant recipients, HCMV DNA was detected in one or more consecutive blood samples. HCMV DNA PCR was also positive in one or more samples from eight patients who never developed HCMV-related symptoms. HCMV pp65 antigen was detected almost exclusively in PBL samples from organ transplant recipients suffering from HCMV disease. However, antigenaemia was not detected in four PCR positive patients presenting clinical signs attributable to HCMV infection. Two of the initially HCMV DNA positive samples were not confirmed by retesting and hybridisation. The results of the present study demonstrate that despite the high specificity of nested PCR, HCMV DNA may be detected in the absence of clinical symptoms attributable to HCMV infection. In asymptomatic reactivation, limited replication of viral DNA may be responsible for positive results of PCR without any clinical relevance. In this context, pp65-antigen detection from PBL seems to have a better prognostic value, but is not always detected when clinical symptoms are present.