BACKGROUND AND OBJECTIVES: Cytomegalovirus (CMV) infection continues to be a major complication of bone marrow transplants (BMTs). Administration of leukoreduced unscreened cellular blood products at the bedside has been shown to be effective in preventing CMV transmission via transfusions in CMV-seronegative bone marrow transplant recipients who receive their transplants from CMV-seronegative donors. The aim of this study was to determine whether CMV infection occurred in CMV-seronegative BMT patients who received CMV-seronegative donor marrows and CMV untested blood products leukodepleted at the bedside. DESIGN AND METHODS: We collected data over a 2-year period from patients undergoing allogeneic transplantation who received leukoreduced cellular blood components that were not screened for CMV. All CMV-seropositive patients and donors were excluded from the study. The CMV status of both the donors and the patients was determined before the transplantations. CMV cultures of urine, blood buffy coat, bone marrow samples and bronchial washings were performed if necessary in patients. RESULTS: Thirty-six CMV-seronegative patient-donor pairs were included in the study. Five patients (13.89%) were serologically reactive, but their CMV cultures were negative and they did not show signs or symptoms of CMV infection. These patients received intravenous immunoglobulin and thus could have acquired anti-CMV passively. INTERPRETATION AND CONCLUSIONS: The confidence interval in this study is 0/36 incidence of CMV infection. Our present findings support those of prior studies showing the effectiveness of filtered unscreened blood components as an alternative transfusion support for CMV-seronegative marrow transplant recipients. Studies in larger number of patients are warranted.