Resection of pulmonary tissue for bronchial carcinoma causes a decrease in vital capacity of 15% after lobectomy and 35-40% following pneumonectomy. After operation the lung becomes stiffer and elastic recoil pressure and transdiaphragmatic pressure at TLC increase. Maximum effort tolerance decreases after pneumonectomy with a normal pulmonary artery pressure at rest and an increase in pulmonary artery pressure and in pulmonary vascular resistance on effort, compared to preoperative values. Cardiac output and stroke volume during effort show a decrease after operation with an increase in peripheral arterial blood pressure and in peripheral vascular resistance. Arterial oxygen saturation on effort decreases after pneumonectomy, possibly due to the absolute decrease in diffusing capacity. When comparing resting and exercise values at identical work loads, increases in systemic arterial blood pressure, pulmonary and systemic vascular resistance and arteriovenous oxygen difference were similar although generally less pronounced after lobectomy compared to pneumonectomy; cardiac output, stroke volume and oxygen consumption showed the same tendency to decrease after lobectomy and pneumonectomy.