Bronchiolitis obliterans (irreversible small airway obstruction) is a late complication of heart-lung transplantation. Chronic immune rejection is believed to be the major cause of this complication. Our hypothesis was that denervation might contribute to airway obstruction. To test this hypothesis in the absence of immune rejection, we performed a lobectomy of the upper lobe of the left lung and autologous reimplantation of the lower lobe of the left lung in 13 growing pigs. To serve as age-matched controls, six other pigs had sham left thoracotomy and nine others had a lobectomy of the upper lobe of the left lung alone. Nine to 10 weeks after operation, the animals were anesthetized and the lungs mechanically ventilated. The lobes were then isolated in vivo to measure differential transrespiratory mechanics and volumes. Dynamic compliance was significantly lower in the reimplanted lobe than it was in the contralateral right lung. This was the case after lobectomy of the upper lobe of the left lung or sham thoracotomy. Dynamic resistance was significantly higher in the reimplanted lobe than it was in the contralateral right lung and in the left lung after sham thoracotomy. Measurements of extravascular lung water, dry lobe weight, alveolar cross-sectional area, and volumetric proportions of lung parenchyma and alveolar spaces did not demonstrate abnormal structural growth after reimplantation. We conclude that lobectomy of the upper lobe of the left lung and autologous reimplantation of the left lower lobe leads to adverse changes in flow-dependent measurements of airway patency. Changes in bronchomotor regulation imposed by denervation may contribute to airway obstruction after heart-lung transplantation.