Using the standard strains such as Sh. flexneri 2a and St. albus, that are stocked in our laboratory, the author studied the influences of Fe⁺⁺, Fe⁺⁺⁺ and αα'-dipyridyl on the oxidation of various substrates, especially that of glucose, and obtained the following results: 1. Fe⁺⁺ and Fe⁺⁺⁺ promotes the complete oxidation of pyruvate in the course of the glucose oxidation, whereas αα'-dypyridyl acts as to inhibit the oxidation. 2. One of the actions of Fe⁺⁺ and Fe⁺⁺⁺ seems to be the enzymatic reaction involved in high energy phosphate compounds. 3. It appears that first Fe⁺⁺⁺ is reduced to Fe⁺⁺ in the process of the substrate oxidation by bacteria and then it begins to act.