The histochemical behaviour of alkaline phosphatase, adenosintriphosphatase, acid phosphatase and acetylglucosaminidase activities was studied in rat kidney treated with Chloromeridrin Hg. In these experimental conditions it was found that the nephrocytes in the proximal convoluted tubule present changes in the enzymatic activities examined, generally proportional to the doses employed. With lower doses of radionuclides, the histoenzymatic changes have a local character and are completely reversible after a month. With higher doses they take on a more extensive character and persis to some extent one month after treatment. These findings suggesti that Hg could be used clinically with due precautions.