A case of apparent red cell (RBC) autoimmunity due to anti-c is described in the recipient of a cadaveric renal transplant. Although the patient suffered little hemolysis as a result, a strong direct anti-c agglutinin was detectable on the patient's RBCs 8 days after transplantation and in his serum only 4 days after transplantation. We believe that the antibody was produced by passively transferred B lymphocytes in the donor kidney, and that the recipient may have been protected from more serious hemolysis by immunosuppressive agents administered at the time of transplantation. The donor received multiple transfusions before transplantation, but his serum lacked anti-c in a screen performed shortly before his death. This case raises the possibility that donor alloantibodies to other Rh antigens on recipient RBCs can arise after transplantation, if the donor has been transfused.