Bronchospirometric studies of the ventilatory function in 200 patients with pulmonary cancer inducated a dependence between functional losses in the involved lung and tumor localization, and the functional importance of the bronchus involved. A central localization of the tumor results in more pronounced functional losses in gas metabolism, in particular, that, as evidenced by rheographic findings, is conditioned by both the reduced ventilation and blood flow in the affected lung. The results of investigations have indicated that in 80% of patients the rate of functional losses and their distribution between the involved and intact lung allowed an accomplishment of an operative intervention such as pneumonectomy.