With the purpose to see the effects of thoraco-surgical treatment on leucocyte function in pulmonary tuberculosis, the author examined the picture, wandering velocity, and phagocytesis of leucocytes in the patients with pulmonary tuberculosis, starting before operation and continued for three months; and obtained the following results; Pulmonary Resection 1. The total leucocyte count: The effect of surgical treatment is most marked on the day of operation, namely the leucocyte count increases up to 10,000-20,000, but rapidly decreasing thereafter, it returns to the pre-operation level by the 20th day and it keeps its normal level thereon. And the increase or decrease in the leucocyte count more or less parallels with the extent of operation and the increase or decrease in the neutrophil count. 2. Fluctuations of various leucocytes: The change in the neutrophil count takes about the same course as that of the leucocyte total. The eosinophil count begins to disappear immediately after operation and appear on the third day; thereafter, it returns to the pre-opsration level. As for the basophil count, with the exception of a transient increase on the third day, it shows no fixed trend neither monocytes. As for the percentage of lymphocytes, a marked decrease can be observed on the day of operation, and thereafter, recovering gradually, it takes somewhat the opposite course to that taken by neutrophils, but the absolute count shows no marked change. 3. The leucocyte function: The wandering velocity of leucocytes is accelerated on the day of operation, and declining thereafter, shows its minimum on the third day after operation, but by the 10th day it returns to the preoperation level, thereon it surpasses that level. The phagocytosis of leucocytes is promoted on the day of operation, and falling down to its minimum on the second day after operation, it returns to the preoperation level on the fifth day, and later it surpasses that level. Namely, on the day of operation leucocytes show what Sugiyama calls "progressive left-shift of the nucleus", and the second day as the turning point their picture is transferred to "regressive left-shift of the nucleus", and it returns to that before operation on the 5th to 10th day. Thereafter the leucocyte function is accelerated, and also it is obvious that the phagocytosis of leucocytes is more responsive to reaction than the wandering velocity Thoracoplasty Leucocyte findings and their function by this treatment show rather similar tendency observed in the Pulmonary resection. The improvement up to the 20th day after the treatment in this case, however, is relatively more rapid than that in the Pulmonary resection, while after one month the improvement is a little inferior to that by the former method. Group Showing Postoperative Complication About the 5th day after operation the decrease in the leucocyte count of this group is less than that of the group with good postoperative improvement, and also the recovery of the leucocyte function is slower, showing no return to the preoperation level. Summarizing the above, the thoraco-surgical treatment essentailly acts as a stress on patient, and the response to the operation appearing most markedly on the day of operation, the direct influence of operation disappears by the 20th day. Moreover, the group with postoperative complication the recovery of leucocyte findings and their function is prolonged. It is believed that the follow-up examinations of the leucocytes and the leucocyte function offer some important clues for the determination of postoperative conditions.