Polyol dehydrogenases, i.e., sorbitol dehydrogenase, adonitol dehydrogenase and mannitol dehydrogenase of rabbit bone marrow were studied. Bone marrow was homogenized and the distribution of the enzyme activity in cytosolic, mitochonrial and nuclear fractions was measured. Sugar dehydrogenase activity in the crude preparations was also observed. The results obtained were as follows: 1. Sorbitol dehydrogenase activity which reduces D-fructose in the presence of NADH to D-sorbitol was localized in the mitochondria) fraction. The reverse reaction was inactive in both cytosolic and mitochondria) fractions. 2. Adonitol (ribitol) dehydrogenase activity (196 units/g wet tissue) was found to be approximately 3 times higher than that of sorbitol dehydrogenase and 40 times higher than mannitol dehydrogenase. 3. Mannitol dehydrogenase activity was very low (4.2 units/g wet tissue) and 88% of total activity was found in cytosolic fraction. 4. Sugar dehydrogenase were also examined in the crude preparation of bone marrow. he enzyme was most active with rhamnose (20.14 units/g wet tissue), but a number of other sugars was also good substrate. Dehydrogenation was effective in the following order of activity: rhamnose>xylose>lactose>glucose>mannose>galactose>maltose Trehalose did not serve as substrate.