Between May, 1981, and December, 1984, thirteen combined heart-lung transplants were performed in 12 patients for the treatment of Eisenmenger's syndrome. The age range of the recipients was 22 to 42 years. Two patients had undergone previous open cardiac operations; in addition, one had had closure of a persistent ductus arteriosus, one an open lung biopsy, one a pulmonary artery banding, and one patient received a second heart-lung transplant after 3 years. Four recipients died before hospital discharge, one at operation and three at 4, 10, and 33 days after operation. Early symptomatic results and cardiopulmonary function were excellent in all of the survivors. Two patients died 14 and 15 months after transplantation of accelerated graft arteriosclerosis and respiratory failure, respectively, and six remain alive 7 to 44 months after transplantation. Four of these surviving patients and the two patients who died late subsequently had major pulmonary complications. Symptoms included progressive breathlessness, cough (often productive), and fever with physical signs of diffuse crepitations and expiratory rhonchi. Serial pulmonary function tests showed progressive obstructive physiology in all six patients with superimposed restrictive defects in four. Histologic examination of tissue from open lung biopsy or autopsy displayed bronchiolitis obliterans in five of these patients, one of whom required retransplantation. It is possible that these late changes are the result of rejection, since similar changes in one other patient have now been reversed with augmented immunosuppression. Further understanding of the causes and manifestations of late pulmonary deterioration should improve the late functional results of this operation for Eisenmenger's syndrome.