Using St. aureus, sh. flexneri 2a and Sal. typhi 57, the author carried out the studies on pentose formation from glucose or other substrates. The following results were obtained. 1) A fairly large amount of pentose was formed and accemulated from glucose, gluconate, glycerophosphate, lactate or pyruvate in every strain of the bacteria tested in the presence of AM or DNP in corcentrations of 3×10(-4) and 10(-3)M. 2) Pentose was supposed to be formed from glucose through gluconate in the case of St. aureus, but was probably formed through C(3)-comound in the case of Sh. flexneri 2 a and Sal. typhi 57. 3) It was postulated that AM and DNP inhibited the break-down of pentose to C(3)-compound; however, did not inhibit the synthesis of pentose from C(3)-compound. Part Ⅱ Effect of Changes in Culture Condition on Pentose Formation With the use of Sh. flexneri 2 a as test organism, the author investigated the effect of changes in culture condition on pentose formation and obtained the following results. 1) The bacterial cells cultured on glucose added media showed further oxidation of pyruvate to a less extent and was able to produce pentose to a greater extent from glucose and C(3)-compound in glucose metabolism. 2) The bacterial cells cultured on glucose and α, α-dipyridyl added media was more inferior in the further oxidation of pyruvate, and was more promoted pentose formation rate. 3) Pentose was produced to a greater extent under anaerobic condition than under aerobic condition. 4) From theee results, it could be stated that the suppresion of pyruvate oxidation accelerated the reaction rate which produced pentose from glucose through C(3)-compound.