From January 1975 to December 1986, 415 patients were operated for primary lung cancer. Postoperative pulmonary complications were observed in 83 patients and among them 48 patients (57.8%) suffered from difficulty in expectoration. Postoperative expectoration mostly depends on the ability of coughing. To evaluate cough dynamics, expiratory flow-rate and volume at voluntary maximal cough were measured. The more expiratory flow rate and volume a cough has, the more effective it is for expectoration. In those patients with decreased FEV1.0, or respiratory muscle weakness because of emaciation and aging, or severe pain in the wound, the cough dynamics was decreased. By cleaning retained secretions in the respiratory tract, postoperative pulmonary complications would be prevented. However in cases where the decrease in postoperative cough dynamics is predictable, application of limited resection should be considered as well.