Part Ⅰ Effect of Added Substance to the Media on Catalase Activity Using Sh. flexneri 2 a and Sal. typhi 57 as test organism, the author studied the effect on calase activity of bacteria by adding a certain kind of substance into culturing media, the following results were obtained. 1) The catalass activity was not influenced by the addition of lactate, pyruvate or succinate into media, but was decreased by addtion of glucose. 2) A marked decrease in the catalase activity was observed by addition of KCN or NaN(3), in dilution of 1/3×10(-4)M; whereas no change in other enzyme activity was observed by the addition of these substance. 3) The addition of α, α'-dipyridyl or oxine, in dilutions of 20-30 mg/L, showed marked decrease in oxidative ability of bacteria of pyruvarte, and the decrease in catalase activity was simultaneously observed only in Sh. flexneri. Part Ⅱ Oxidation of glucose and alanine by catalase deficient bacteria Using Sh. flexneri 2 a, Sh. dysenteriae 4 and D. pneumoniae Ⅱ, the author studied the enzymatic properties of the catalase active and inactive bacterial cells mentioned above by means of volumetric studies of glucose and alanine oxidation and also studied the effect of these cells on normal or acatalasemic erythrocytes, especially on hemoglobin of the erythrocytes. The following results were obtained. 1) As the cells of Sh. flexneri 2 a grown on KCN or NaN(3) added nutrient agar media was lacking catalase activity, the organism could'nt decompose H(2)O(2) produced throuth the course of glucose or alanine metabolism. So formed pyruvate by the metabolism was oxidized by H(2)O(2) inversely. And hemoglobin was oxidized to methemoglobin, when erythrocytes were added to the reaction media. 2) Sh. dysenteriae 4 is failing catalase and the production of H(2)O(2) was not detected at all or only scantily on the cells grown on any kind of media. 3) D. pneumoniae Ⅱ is also failing catalase, but the production of H(2)O(2) was remarkably high.