Résumé : Hemolysis due to donor-derived red cell antibodies is a potential complication after minor ABO-mismatched solid organ transplantation. It has also been described in Rh-positive recipients receiving organs from previously isoimmunized Rh-negative donors. We report on a group O, Rh(D)-positive patient who received a heart-lung transplant from a group O, Rh(D)-negative donor presenting an anti-D antibody. Severe hemolytic anemia developed in the early postoperative period and lasted for 3 mo. Anti-D antibodies that were of donor origin were found in bronchoalveolar lavage fluid and serum. In addition, using the polymerase chain reaction for human leukocyte antigen class II genotyping, we were able to demonstrate the presence of a mixed population of donor and recipient cells in the lungs and the peripheral blood of the recipient. The chimeric state in the blood persisted until at least the fifty-seventh postoperative day. This first case report of hemolysis due to Rh(D) antibody after heart-lung transplantation emphasizes the need for routine red cell antibody screening of donors and for close monitoring of signs of red cell destruction in the recipient in cases of pretransplant donor isoimmunization.