Unilateral lung transplantation has provided effective short-term therapy in adults with end-stage lung disease. Rejection continues to be the most common cause of transplant failure. Living-related lung transplantation may decrease the recipient immune response. The purpose of this study is to test the technical and physiological feasibility of living-related lobar lung transplantation from adult beagles into beagle puppies in a chronic model. Twenty purebred adult beagle donors underwent left thoracotomy with harvest of the left lower lobe using cold perfusion of the pulmonary artery and cold immersion. Twenty recipient purebred beagle puppies from the same colony underwent left thoracotomy, left pneumonectomy, and implantation of the donor adult lobe. Anastomoses were performed in sequence: pulmonary vein to left atrium, bronchus, pulmonary artery. Postoperative immunosuppression was with Cyclosporine. Respiratory function of the implanted lobe was evaluated by pulmonary angiography and during balloon occlusion of the right pulmonary artery with arterial blood gases 1 month after transplantation. Ten recipient puppies died of rejection (4), infection (3), or bronchial dehiscence (3) prior to angiography. Seventeen pulmonary angiograms in 10 surviving animals showed normal left pulmonary arterial blood flow (2), diminished left pulmonary arterial flow (5), and occluded left pulmonary artery (3). In two recipients balloon occlusion of the right pulmonary artery was performed and respiratory function was maintained solely by the transplanted lobe for 2 days in one recipient and for 30 minutes at 1 month and 2 months postimplant in a second recipient. Living-related lung transplantation of adult beagle lobes into pneumonectomized beagle puppies is technically feasible. High mortality rates in a chronic model are related to infection and rejection.(ABSTRACT TRUNCATED AT 250 WORDS)