Background. Organ donors and transplant recipients are routinely tested for ABO compatibility. ABO-identical organs are preferred, but occasionally the use of an ABO-compatible but nonidentical donor is clinically warranted. In heart-lung transplantation, the incidence of hemolysis from donor-derived anti-ABO antibodies is as high as 70%. The incidence of hemolysis for lung- only transplantation is not known. Our current posttransplantation transfusion policy for ABO-compatible but nonidentical lung-only transplant recipients is, when indicated, to use donor ABO group red blood cells. Methods. To evaluate the efficacy of our transfusion policy, we reviewed our experience from 1986-96. One heart-lung transplant, four single lung transplant, and three bilateral single lung transplant recipients received ABO-compatible but nonidentical organs. Results. The heart-lung transplant recipient developed a positive direct antiglobulin test (DAT), with anti-A eluted, and severe hemolysis on postoperative day 8 requiring plasma and whole blood exchange. Four of six lung-only transplant patients tested developed a positive DAT with anti-A eluted. Two early lung-only patients, who did not receive donor ABO group red blood cells, demonstrated clinical and laboratory evidence of hemolysis. Three bilateral lung transplant recipients were followed prospectively. The first patient had a negative DAT. The next two patients developed positive DATs on postoperative day 8 and 10, respectively. No evidence of hemolysis was detected in any of these cases. Conclusions. These results confirm that donor-derived anti-ABO antibodies develop with lung-only transplants. Our current transfusion policy is justified for both heart-lung and lung recipients of ABO-compatible but nonidentical organs. A high index of suspicion for donor-derived antibody causing hemolysis and communication with blood bank personnel are mandatory in this setting.