Changes in abdominal (delta AB) and rib cage (delta RC) movements, and in vital capacity, were compared between 23 patients undergoing upper or lower abdominal surgery at 1, 3 and 7 days after surgery. Diaphragmatic index was obtained by measuring the relative abdominal motion (delta AB/delta AB + delta RC) using magnetometers. Electrical activity of abdominal muscles was assessed using needle electrodes after upper abdominal surgery in four additional patients. After upper abdominal surgery, the vital capacity and the diaphragmatic index were markedly reduced for 1 week. No abdominal muscle activity was observed at day 1. After lower abdominal surgery, the vital capacity returned to the normal range within 3 days of operation, without any diaphragmatic impairment. These findings substantiate the role of diaphragmatic dysfunction in postoperative reduction in vital capacity observed after upper abdominal surgery.