An attempt has been made to observe the effects of chromium on a few enzymes, viz. alkaline phosphatase, acid phosphatase, glucose-6-phosphatase and lipase, in the kidney of the rat (Rattus rattus albino) by means of histochemical and biochemical criteria. Administered as potassium chromate in the diet, it was found to inhibit the activity of these renal enzymes; moreover, characteristic differences were observed in their anatomic localization. The possible effects of chromium on the level of enzyme protein and the state of the cellular organelles, together with modifications of biochemical processes such as phosphorylation, adenylation and oxidative phosphorylation, are discussed.