Local cerebral blood flow was measured with hydrogen clearance method in fifteen dogs and compared to direct measurement obtained by Michenfelder's venous out flow method. The sagittal sinus was exposed by a midline frontooccipital incision and extensive craniectomy. A tappered catheter was passed in to the superior sagittal. sinus. For measuring hydrogen clearance, platinum wire electrodes with a red tip of 0.5 mm in length and 0.3 mm in diameter were introduced into the parietal and occipital cortex. About ten percent hydrogen gas was given directly into the endotracheal tube for three to five minutes and the obtained clearance curves were transferred to semilog graph papers. Total cerebral blood flow was caliculated by bicompartmental analysis and compared to the two minutes initial slop index. The results are as follows. 1) A linear regression analysis of flows caliculated from the initial slope and bicompartmental analysis shows a high correlation coefficient. 2) There is a high correlation between flows caliculated from electrodes used at the same experiments. 3) Cerebral blood flow from the initial slope measured by hydrogen clearance method shows a high correlation wit flows caliculated from Michenfelder's venous out flow method.