Human cytomegalovirus (HCMV) was investigated in peripheral blood leukocytes (PBL) of 52 immunocompetent patients (40 pregnant women) with primary HCMV infection by quantitative determination of pp65 antigenemia, viremia, and leukoDNAemia. pp65 antigenemia was detected in 12 (57.1%) of 21, 4 (25%) of 16, and 0 of 10 patients examined 1, 2, and 3 months after onset, respectively. Viremia was detected in 5 (26.3%) of 19 patients during the first month only. LeukoDNAemia was detected in 20 of 20, 17 (89.5%) of 19, and 9 (47.3%) of 19 patients tested 1, 2, and 3 months after onset, respectively. Four (26.6%) of 15 patients were still DNAemia-positive at 4-6 months, whereas none were positive at >6 months. HCMV was not detected in PBL of 20 HCMV-immune donors or of 9 seropositive subjects with recurrent infection. Virus levels were low by all assays and did not correlate with clinical course of infection, intrauterine transmission, or severity of outcome. Invasive procedures in the presence of maternal leukoDNAemia did not seem to interfere with vertical transmission of HCMV infection.