In order to establish the effects on oxydative degradation of glucose and practical utility of chloromycetin as inhibitor, the author studied the effect of chloromycetin on O(2) uptake of the microorganisms and the cooperative inhibition by the combined use of chloromycetin and other inhibitor. Sh. flexneri 2a, Sh. flexneri 3 a, Staphy. aureus and Staphy. albus, all taken from the departmental stock, were used in this work. The following were obtained. 1) The O(2) uptake of organisms were not affected in the presence of dilute chloromycetin, but the uptakes were decreased in 30-40% with 10(-3) M of chloromycetin in either substrates, glucose, lactate. pyruvate or succinate. With the concentration of 3×10(-3) M the decrease of the uptake reached to 60-70%; moreover, the suppression was most serious on the uptake of pyruvate. 2) In the case of Sh. flexneri 2 a and Sh. flexneri 3 a, the simultaneous use of chloromycetin and NaN3 showed marked inhibition on the O2 uptake compared with use of each of them. But in Staphy. aureus and Staphy. albus, it was not observed such cooperative inhibition like this.