Abstract
1. Heterogeneity of xylulose reductase activities was proved by electrophoresis on cellulose acetate of rat and human liver or kidney homogenates. Two separable forms of xylulose reductase activities were found in these tissues.
2. One is associated with the mitochondria and the other is mainly in the supernatant fraction of the cells.
3. An aqueous extracts of acetone powder of rat and human liver showed also two xylulose reductase activities.
4. The enzyme of one fraction was easily inhibited by trypsin.
