Resting tidal volume and vital capacity were measured daily in 5 patients with acute quadriparesis during the first 7 to 10 days of their hospitalisation. On admission, vital capacity was significantly reduced to 26% of the predicted value (p less than 0.001). This increased significantly over the study period to 33% of the predicted value (p less than 0.02). Expiratory flow rates, measured on one occasion during the study period, showed similar decrements. Tidal volume and vital capacity were also measured immediately following administration of intermittent positive pressure breathing (IPPB). Although the lung volume achieved during IPPB was significantly higher than resting values of tidal volume and vital capacity (p less than 0.001), tidal volume returned to baseline values as soon as IPPB was ceased. Vital capacity remained significantly higher than baseline values at this stage (p less than 0.02), although the mean increase in vital capacity immediately following IPPB was only 43 mls. Acute quadriparesis is associated with a severe ventilatory impairment which includes a reduced vital capacity and expiratory flow rates. IPPB has a positive effect on lung volume whilst it is being administered. Immediately following treatment, this effect does not appear to be sustained at a level which would be considered clinically significant.