Transplantation of the heart and both lungs is the only therapy that can be offered to certain patients with end-stage pulmonary vascular disease. Our experimental experience with the baboon is presented. Fourteen allotransplants were performed, 12 recipients (inadequately immunosuppressed with cyclosporin A and azathioprine) surviving between 4 and 29 days. In 11 cases death resulted from acute rejection which predominantly involved the lungs, the heart being spared in 10 cases; the remaining death was from bronchopneumonia. Two autotransplanted baboons survived until sacrificed at 6 months. Indications for the operation, selection of both the recipient and the donor, and recent results at other centres are briefly reviewed. It would seem that this operation is recommended in selected patients with idiopathic pulmonary hypertension or Eisenmenger's syndrome whose condition is deteriorating and in whom no other form of therapy is applicable.