In order to evaluate ventilatory function of the remaining lung after lobectomy, using dogs, we measured the pressure-volume curve of the right lower lobe separately from the other lobes. The right lower lobe bronchus was surgically separated from the other bronchi and the expiratory volume of the right lower lobe was measured independently. The dogs were put in an airtight box. Transpulmonary pressure and expiratory volume in the right lower lobe were measured before lobectomy, after the left upper lobectomy and subsequently after the right upper and middle lobectomy. As a result, the esophageal pressure at endoexpiratory state became more subatmospheric following the lobectomies and the pressure-volume curves of right lower lobe shifted down to the right. Though the right lower lobe was intact after surgery, the pressure-volume curve shifted. This might be caused by the imbalanced postoperative volume of the lung and thoracic cage, and it is one of the problems remaining after lobectomy.