Many of the alterations in lung function that occur after upper abdominal surgery are attributable to reduced diaphragmatic activity. This study was undertaken to determine whether incentive spirometry produces a voluntary activation of diaphragmatic movement in patients with postoperative diaphragmatic dysfunction. Inductance plethysmography was used to measure the tidal volumes of the abdomen and chest in eight women before cholecystectomy and on the first and third postoperative days. In resting patients the relative contribution of the abdominal compartment decreased from 0.520 +/- 0.100 preoperatively to 0.274 +/- 0.265 on postoperative day 1 (p less than 0.01), reflecting the effect of surgery on diaphragmatic function. Inspiratory flow (an index of inspiratory drive) was unaltered by surgery during both resting and incentive spirometry breaths, despite changes in tidal volume. Preoperatively, incentive spirometry increased the tidal volume of the abdominal compartment from 141 +/- 26 ml to 285 +/- 188 ml (p less than 0.005) as a result of increased diaphragmatic movement. This effect was not seen postoperatively; instead, postoperative patients responded to incentive spirometry by increasing the tidal excursion of the chest compartment (158 +/- 37 to 630 +/- 253, p less than 0.005), without any increase in abdominal tidal volume. Thus, incentive spirometry failed to increase diaphragmatic movement in postoperative patients.