We have investigated the localization and demonstration of sorbitol dehydrogenase activity in the rat kidney by comparative histochemical-electrophoretical technique. Under histochemical conditions an adequate demonstration of the activity of the sorbitol dehydrogenase in native sections is possible by membrane incubating technique in presence of PMS and KCN. In the glomerulum the strong and uniform reaction with regard to the specifity is not clear. In the glomerula of semithin sections from glutaraldehyde fixed, incubated and Epon-embedded cryostate sections the reaction product is localized predominantly in the maesangium cells. By micropolyacrylamidgel gradient electrophoresis of the supernatant from the kidney cortex and of isolated glomerula 2 sorbitol dehydrogenase fractions were found. The results are discussed in connection with the specifity of the reaction.