Pulmonary function criteria for pulmonary resection, other than pneumonectomy, have not been previously described. A series of 500 consecutive pulmonary resections to which specific pulmonary function criteria were applied in determining the amount and the extent of feasible resection of the lung are presented. By application of these criteria, an accurate assessment of the type and extent of pulmonary resection a patient can tolerate without expected mortality can be made. With utilization of these criteria, the operative mortality for segmental resection was 0.2 per cent; for lobectomy, zero per cent, and for pneumonectomy, 4.4 per cent.