Comment: If partial lobectomy is confined to the extirpation of the major surgical divisions of the lungs, there is little danger of /[See figure in the PDF file/] failure to identify the segment. It would be easy, however, to perform an incomplete operation when removing one or more of the minor divisions. It appears, therefore, that if there is any question concerning the amount of lung tissue to be excised, the surgeon is obligated to error on the radical side. Inadequate extirpation of diseased tissue will cast disrepute on the principal of partial lobectomy, which is sound when employed properly. The excision of one or more of the minor pulmonary segments will have limited application and must be reserved for cases in which the lesion is peripheral and sharply localized. Preoperative localization of the disease must coincide exactly with the findings when the lung is exposed at operation. It should be recorded categorically, that neoplasms of the lungs should not be treated by partial resection of lung tissue. The practice of local excision of a mass of undetermined origin will be useful in establishing a positive diagnosis and will undoubtedly lead to an increasing number of successful operations for peripheral /[See figure in the PDF file/] lung tumors. If, however, a neoplasm of the lung is found when partial lobectomy is performed, for diagnostic purposes, a radical operation should be undertaken regardless of the apparent clean removal of the localized mass. An example of a suitable case for partial lobectomy with removal of a minor division of the lung is illustrated in Figure III (A) , Figure III (B) . The relative operative risks of partial and complete lobectomy are probably about the same. My own experience has been limited to the performance of 17 partial lobectomies. In this group there was one death. During the same period 55 complete lobectomies were performed and in approximately half of these, it was necessary to remove two lobes. There was one death in the latter group. These figures, however, are of no statistical value. Assessment of the influence on the immediate mortality of partial as compared to complete lobectomy must await further experience. The only significance of the principle is that important amounts of lung tissue may be conserved in selected cases.