In 250 patients with pulmonary tuberculosis who were preoperative or undergoing no operation, and in 5 normal persons, the function of ventilation was examined since March 1953, and the following results were obtained. 1) The function of ventilation in normal persons at rest was almost the same as the report of other investigators, the proportion of vital capacity of the right to left lung being 51.2/48.8. 2) In pulmonary tuberculosis, slight cases presented similar function to that of normal persons, while the functional disturbance was marked as the lesion in pulmonary parenchyma was extensive. The functional disturbance. however, was not so prominent that many serious cases still presented standard values. 3) In pleural callosity and bronchial stenosis the function of ventilation was markedly disturbed. In the former a restrictive disturbance of ventilation was observed, while in the latter an obstructive disturbance as well as a tendency toward emphysema was recognized, both of which were marked, according as the fibrosis of the pulmonary parenchma became extensive. In general, severe cases of pulmonary tuberculosis displayed a mixed type of the obstructive and restrictive disturbances of ventilation due to the coexistence of the extrapulmonal factor and bronchial lesion described above. 4) Functional tests such as hypoxia and physical exercise are highly significant for the purpose of demonstrating potential disturbances which are not recognized at rest. In these tests it was found that slight or moderate cases with pulmonary tuberculosis still possessed sufficient reserve capacity of ventilation, while severe cases who did not reveal marked hypofunction at rest becauseof the compensatory activity, often displayed decompensation following these loading cited above, presenting a decreased oxygen saturation in the arterial blood, which was especially marked in cases with pulmonary fibrosis. The oximetric value in the test of respiratory arrest is not found sufficient for the index of the evaluation of the function.