The cases of pulmonary resection under endotracheal anesthsia of closed circulation were divided into two groups, i.e. the normal blood pressure group and the hypotensive group, and the glomerular filtration rate (C.F.R.) and the tubular reabsorption rate (T.R.R.) were evaluated in each group. 1) G.F.R. markedly decreased during operation in both groups and restored almost to the preoperative G.F.R. after recovery. 2) The hypotensive group showed a little more marked decrease of G.F.R. during and after operation than the normal group. The volume of urine showed a similar change to G.F.R. 3) T.R.R. showed no change before, during and after operation proved to be due to the decrease of G.F.R.