The histochemical behaviour of succinic dehydrogenase, isocitric dehydrogenase, acid phosphatase and acetylglucosaminidase activities was studied in rat liver treated with Au198-colloidal. In these experimental conditions it was found that the hepatocytes 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. These findings suggest that Au198 could be used clinically with due precautions.