By using H37 Rv and H3 7R astrains of human tubercle bacillus, a series of comparative studies have been made on the dehydrogenase reactions by the intact cells possessing the acid-fast natures and by the cell-free extracts without that nature. The results are as follows: 1) In both strains, in the case of cell-free extracts without the addition of substrate, dehydrogenase activity decreases to about 1/2 of that of the intact cells. 2) With the use of hexose as substrates, the dehydrogenase activities of the cell-free extract of H37Rv strain are somewhat higher than those of intact cells, while in the case of H37Ra strain the activities of the cell-free extract are lower than those of intact cells. 3) The activities of the cell-free extracts to pyruvate and lactate are, in both strains, markedly lower than those of intact cells, whereas in the case of H37 Rv strain the malate dehydrogenating activity is greater in the from of cell-free extract than in intact cells. 4) To histidine, the activity of the cell-free extracts of both strains is far greater than that of intact cells.