By measuring the oxygen consumption in the sternal bone marrow of various leukemias definitely diagnosed on the basis of their bone-marrow tissue culture, the author obtained the following results. 1. In leukemia the oxygen consumption of 0.2 cc/hr sternal bone marrow shows an increase as compared with that of normal persons, and the degree of this increase differs according to the form of diseases. The grade of such an increase is in the descending order of that in acute myelogenous leukemia, chronic myelogenous leukemia, acute lymphocytic leukemia, monocytic leukemia and chronic lymphocytic leukemia. Xo(2)/K in comparison with that in the normal case is increased in acute myelogenous leukemia and monocytic leukemia, but in chronic myelogenous leukemia it is somewhat decreased, and in acute and chronic lymphocytic leukemia it is markedly decreased. Qo(2) is increased in all leukemia as compared with that of normal case, and its increase is in the descending order of that in monocytic leukemia, acute myelogenous leukemia, acute lymphocytic leukemia, chronic myelogenous leukemia, and chronic lymphocytic leukemia. 2. There is a parallel relation between the oxygen consumption, the nucleated cell count, and the immature cell percentage of the bone marrow, and moreover, in chronic myelogenous leukemia at remission due to the treatment the oxygen consumption is also reduced. 3. As for the oxygen consumption of peripheral erythrocytes in chronic myelogenous leukemia it is at the normal level, but in all others it is slightly reduced.