An exercise tolerance test with a bicycle ergometer was carried out in 40 patients prior to pulmonary resection. During the test,expiratory gas was analyzed, and the alterations in the blood gas level and lactic acid value were studied. Nine patients had postoperative cardiopulmonary complications, and 31 had no postoperative complications.It was found that both Vo(2) max and Vo(2) max/body weight were good parameters for indicating significant differences between patients with and patients without postoperative complications. Patients with a Vo(2) max value less than 1100ml/min and/or Vo(2)max/body weight below 20ml/min/kg after an exercise tolerance test with a bicycle ergometer have a high risk of developing postoperative cardiopulmonary complications.