Pre- and post-operative exercise tests and unilateral pulmonary artery occlusion tests were performed on 15 surgical patients with pulmonary cancer. The relationship between these cardio-pulmonary parameters and exercise tolerance was studied, and pulmonary functional resectability was discussed. Pre- and post-operative anaerobic thresholds correlated with driving pressure (D.P: pulmonary artery pressure--pulmonary wedge pressure), and the pulmonary vascular-resistance index (PVRI). From the regression line and post-operative energy metabolic ratio, the standard limitation point of pulmonary resection can be estimated, (D.P = 22.6 mmHg PVRI = 621 dyne.sec.cm-5.m2). These data yielded a pulmonary pressure = 33.4 mmHg, total pulmonary vascular resistance index = 885 dyne.sec.cm-5.m2. These correlations were obtained because D.P and PVRI indicate the over all condition of the pulmonary vascular bed, gas exchange, ventilation and cardiac function. These data were in close agreement with previous results pertaining to the above indications. Unilateral pulmonary occlusion testing predicted the post-operative exercise tolerance of patients undergoing lung resection.