Impaired exercise capacity in adults with moderate scoliosis. We measured lung function and exercise tolerance in 15 adults with moderate kyphoscoliosis (thoracic curvatures between 25 degrees and 70 degrees, mean +/- SD = 46.93 degrees +/- 14.02 degrees). Forced vital capacity showed a slight reduction from values predicted from age and sex matched control subjects (3.39 +/- 1.06 vs 4.06 +/- 0.82 L, p less than 0.05). However, exercise tolerance was significantly lower than previously reported in healthy adults (VO2max = 31.60 +/- 9.12 vs 37.07 +/- 4.91 ml/kg/min, p less than 0.05). Despite the reduced exercise tolerance, the ratio of maximum tidal volume to vital capacity (VTmax/VC) was similar to that observed in healthy adults. The mean dyspnea index (VEmax/MVV) was also normal at 69.4 +/- 19.0. Hypoxic and hypercapnic ventilatory responses were within predicted normal limits at 0.67 +/- 0.37 L/min-1 fall in SaO2-1 and 1.67 +/- 0.92 L/min-1 mm Hg PCO2(-1). We conclude that the impairment of exercise performance found in adults with moderate scoliosis cannot be attributed to any important ventilatory limitation, abnormality in lung volume, or impaired chemoreceptor sensitivity. We suggest that the reduced VO2max likely arises from deconditioning and lack of regular aerobic exercise. 