OBJECTIVE:To evaluate the clinical usefulness of cytomegalovirus (CMV) antigenemia assay among liver transplant recipients in Samsung Medical Center. MATERIALS AND METHODS: All recipients of liver transplantation during the period from Jan. 1996 to Aug. 2003 were enrolled. Medical records and microbiologic data for CMV infections were reviewed retrospectively. RESULTS: All 284 enrolled patients received livers from CMV seropositive donors, and 272 recipients (95.8%) were CMV seropositive before transplantation. One hundred thirty three recipients (46.8%) had evidences of CMV reactivation. Among patients with CMV reactivation, 40 recipients were symptomatic (30.1%) and 12 patients had organ-specific CMV diseases. Most of the CMV infections occurred within 180 days after transplantation except for 9 patients (6.7%). Among the antigenemia positive patients, the mean number of CMV antigen-positive WBC was 19.36 per 200,000 cells (19.36+/-37.64 cells). The mean duration of CMV antigenemia was 8.72 days (8.72+/-9.99 days). Peak value of CMV antigenemia was significantly higher in symptomatic patients compared to asymptomatic patients (P=0.002). Duration of CMV antigenemia was significantly longer (P=0.002) in symptomatic patients. If we would use > or = 5 cells of CMV antigenemia as a cut-off value sensitivity and specificity for symptomatic CMV infections would be 85% and 50% respectively. CONCLUSION: About half of the recipients experienced CMV reactivation, mostly within 180 days after liver transplantation. Thirty percents of reactivation were symptomatic. Five cells per 200,000 leukocytes of CMV antigenemia was the best cut-off level for preemptive treatment.