The deformation of the lung by the chest wall was observed on radiographs of the ribs and interspaces and on morphologic preparations of samples cut from the frozen thorax. The effect of these deformities on the distribution of ventilation and regional lung volume of the underlying lung was determined using Xenon 133. We found that ribs and interspaces deform the lung surface with different radii of curvature, suggesting local differences in pleural pressure and that traction on the thoracic limb caused deformities in the underlying interspaces which were similar to those produced by 20 cm H2O mouth pressure. Xenon 133 showed that these changes in pressure had no effect on the regional volume or on ventilation distribution in the underlying lung. We conclude that changes in pleural pressure produced by localized deformities exert their effect close to the deformity and that the underlying lung responds to the average pressure exerted over a much larger area of the pleural surface.