90 out of 202 lung cancer patients hospitalized for preoperative investigations were scheduled for radical surgery. 15 patients were not operated on because of insufficient lung function data. The operation was performed in 75 patients. The complication rate was 11% and mortality 8%. 7 out of 8 patients who subsequently developed severe complications had fulfilled the criteria for lung resection only after intensive antibronchitic treatment. Nearly all the survivors showed the predicted preoperative minimal lung function values after the operation. The limit of 1000 ml for postoperative FEV1 is justified, since patients with these or larger functional reserves nearly all had a favourable early and late postoperative course, and also because lung function values continuously deteriorate in chronic obstructive lung disease.