Following the previous reports, the author carried out the experiment to elucidate the difference in the pyruvate oxidation and its terminal respiration system between resistant and susceptible Sh. flexneri 2a. 1) The oxidation rate of pyruvate by resistant strain is considerably less at every pH than by susceptible strain. The pH optimum for oxidation of pyruvate of resistant strain is pH 5.6-6.0, whereas that of susceptible strain is pH 7.0-7.5. 2) The consumption rate on pyruvic acid substrate by resistant strain is significantly less than by susceptible strain. 3) Both resistant and susceptible strains oxidizes pyruvic acid via succinate. Pyruvate accumulates during the oxidation of the tricarboxylic acid cycle intermediates such as succinate, malate, fumarate, α-ketoglutarate by resistant and susceptible strains. 4) Aspartic-glutamic transamination has been demonstrated in susceptible strain under aerobic condition with both aspartic acid and glucose added. 5) The oxidation of pyruvate of susceptible strain can be accerelated more rapidly by divalent metal ions such as Mg⁺⁺, Fe⁺⁺, Mn⁺⁺ than that of resistant strain. 6) Panthotenate accerelates more reasonably the respiration of pyruvie acid by susceptible strain than by resistant strain. 7) The significance of these results in relation to the presence of the citric acid cycle in the organism is discussed, and it is considered possible that an significant difference in metabolic activities between resistant and susceptible strains exists in the metabolic pathway from pyruvate to succinate in the citric acid cycle.