Unilateral lung transplantation has become an accepted treatment for patients with end-stage pulmonary disease. Donor shortage, however, is a major limitation, with up to 87% of patients dying of their pulmonary disease while awaiting transplantation. This is especially true in neonatal and pediatric patient populations. The use of organ segments from cadaveric or living donors may provide a solution. The purpose of this study, therefore, was to evaluate the function and hemodynamic response to pulmonary lobar transplantation using a swire model. Five transplants were performed for acute study, while 10 were performed for 6-week survival. The left lower lobe was harvested from a 70- to 75-kg donor animal. The lobe was then transplanted into a 20 to 25-kg recipient following left pneumonectomy. Graft function was determined by pulmonary arterial and venous blood gas analysis. Cardiac output, pulmonary pressure, and pulmonary vascular resistance were measured under two experimental conditions: (I) baseline and (2) with the right pulmonary artery occluded, forcing the entire cardiac output through the lobar graft. All grafts showed excellent acute and long-term function with regard to gas exchange. The lobar grafts, however, were characterized by high pulmonary vascular resistance both acutely and 6 weeks post-transplant. Contralateral pulmonary after) occlusion resulted in hemodynamic instability and right heart failure. No animal was able to be solely supported by the lobar transplant for more than one hour. Thesis results have prompted a bilateral lobar transplant model and current studies are in progress.