Twenty-one patients who underwent pneumonectomy for bronchogenic carcinoma at the Nashville Veterans Administration Hospital from November, 1977, to March, 1980, were evaluated with standard pulmonary function tests preoperatively and postoperatively. Twelve patients had Stage I disease, 4 patients had Stage II, and 5 patients had Stage III disease. The interval between the operative procedure and postoperative testing ranged from 2 to 33 months (mean, 12.4 months). Mean functional loss of pulmonary capacity after pneumonectomy was based on analysis of preoperative and postoperative forced vital capacity (FVC) and initial-second forced expiratory volume (FEV1) indices. The mean functional loss as expressed by FVC was 41.5% after right pneumonectomy and 34.0% after left pneumonectomy. The mean functional loss as expressed by FEV1 was 40.2% after right pneumonectomy and 38.3% after left pneumonectomy. The postoperative functional status of each patient was classified according to the New York Heart Association criteria. Nineteen of the 21 patients were in Class I or II preoperatively. Postoperatively, 10 patients were in Class I or II and 11 in Class III or IV. The results indicate that a postoperative FVC less than 2.5 liters and FEV1 less than 1.5 liters are not compatible with active life.