Activity of Cu/Zn superoxide dismutase (SOD) and catalase (CAT) in gastric mucosa was examined in 12 control subjects and 48 patients with various degree of chronic gastritis. Bioptic specimens of mucosa for enzymologic assays were sampled during gastroscopic examination after overnight fasting. Compared to the control group, a significant increase of SOD activity was observed in samples from superficial gastritis and only insignificant changes in samples from atrophic gastritis, while a remarkable and significant increase in the activity of both SOD and CAT was observed in samples from gastritis after partial gastrectomy. Application of vitamin E significantly reduced activities of SOD and CAT in subjects with chronic gastritis. The authors suppose that the increase in the activities of antioxidant enzymes was caused by an increased formation of superoxide anion radical and hydrogen peroxide, both originating from phagocyting leucocytes in inflamed mucosa. The reduced activity of SOD and CAT after application of vitamin E indicates an inhibition of the formation of active oxygen species in gastric mucosa. Relation of chronic gastritis and elevated concentrations of active oxygen species to gastric carcinogenesis is discussed in the report. (Tab. 2, Fig. 1, Ref. 22.)