Thirty-nine patients with idiopathic scoliosis before and after operation and 20 controls were studied. The minute volume ventilatory response to CO2 stimulation of the scoliosis was not significantly different from that of the control. The restricted tidal volume response to CO2 stimulation appeared to be compensated by the high respiratory frequency and ventilatory drive in order to maintain adequate ventilatory output. The characteristic response of the ventilatory pattern to CO2 stimulation in the scoliotic patients (higher respiratory frequency and smaller tidal volume than the control) was enhanced with increasing the angle of the scoliotic curvature.