The activity to oxidize ethyl alcohol was determined by using the blood of horses, cows and rabbits manometrically with Warburg's apparatus. The data indicated that the corpuscles of horses, cows and rabbits possess the capacity of oxidizing alcohol to a certain extent, while the sera were not capable of oxidizing alcohol. In the rabbits acquiring a tolerance for alcohol by repetitious injection overa period of about two months, the oxidizing activity of corpuscles increases twofold as compared with those of normal rabbits, while the serum remains incapable of oxidizing alcohol. The amount of alcohol oxidized in blood itself, therefore, is calculated at less than one per cent of the total amount of alcohol oxidized in the whole body of rabbit, even after habituation.