In a 12-month prospective study of cytomegalovirus infection on an acute hemodialysis unit, 10 of 80 patients (13%) and none of 26 staff developed active cytomegalovirus infection. Seven infections were coincidental with renal allograft rejection; three occurred 3 to 6 weeks after the transfusion of multiple units of conventional blood into seronegative patients. No person-to-person transmission was documented. In contrast to the effects of transfusing conventional blood, all 21 patients who entered dialysis without detectable cytomegalovirus antibody and received 2 to 10 U of frozen deglycerolyzed erythrocytes (total of 157 U) remained seronegative. Transmission of cytomegalovirus infection with transfusion with conventional blood is probably secondary to passage of leukocyte-borne virus that is lost during the freezing and deglycerolization procedure. Frozen erythrocytes prepared by cytoagglomeration procedures appear to be free of viable leukocytes and appear to carry a minimal risk of transmitting cytomegalovirus infection.