Lung function was evaluated in 13 patients before and after surgical correction of spinal deformity. Lung volumes were unchanged, physiologic dead space fell from 155 to 90 ml, and minute ventilation fell from 9.22 to 7.67 liters/min. Arterial oxygen tension (P02) rose from 87 to 93 mm Hg at rest and from 80 to 85 mm Hg during exercise. The alveolar-arterial Po2 gradient fell from 26 to 20 mm Hg at rest and was unchanged (90 mm Hg) while breathing oxygen. Distribution of ventilation and perfusion, studied with xenon Xe 133, was normal in patients with curves less than 65°. In those with curves exceeding 70°, ventilation in each lung zone was variable. The normal perfusion gradient from upper to lower lung zones was equally reduced both before and after correction.