A randomized multicentre study was conducted to evaluate the effect of anti-CMV hyperimmune globulin in the prophylaxis of CMV infections in CMV seronegative allogeneic BMT patients who received a transplant from a seropositive donor or who had received blood products unscreened for CMV during the treatment before BMT. Twenty-eight patients were included in the study. Thirteen were randomized to receive and 15 not to receive intravenous CMV hyperimmune globulin. A dose of 0.4 g/kg of immunoglobulin was given on day -8 and 0.2 g/kg on days -1, +7, +14, +21, +28, +35, +42, +56 and +70 in relation to the day of transplantation. Among the 15 patients not given immunoglobulin CMV was isolated in three, and two of them developed clinical CMV disease. In addition, one more patient developed CMV antibodies without virus isolation. In five of the 13 patients given immunoglobulin the virus could be isolated, and four of them developed CMV disease. One additional patient showed seroconversion but no other findings of CMV infection. The incidence of acute and chronic GVHD was similar in the two arms. There was no significant difference in survival. In conclusion, the present results do not indicate a beneficial effect of CMV hyperimmune globulin infusions in the prophylaxis of CMV infection or disease in seronegative allogeneic bone marrow transplant recipients from a seropositive donor.