With the use of intact cell suspensions of virulent and avirulent strains of 2 and 6 weeks old cultures in the Sauton media, comparative studies on the dehydrogenating reaction of each substrate, sugars, sugar alcoholes, organic acids, were carried out by Thunberg method. The results were as follows. 1) In the case of the 2 weeks old cells of avirulent strain without addition of substrate, the rate of methylene blue reduction is faster than that in the case of the virulent strain; and the 6 weeks old cells of virulent strain without substrate do not cause decoloration of methylene blue. 2) When sugar or sugar alcohole is used as a substrare, no significant difference in the reduction time can be seen between the virulent and avirulent strains, nor any marked difference among each of the substrates. The rate of reduction by the 2 weeks old cells of avirulent strain, however, is more accelerated than that by the virulent strain by the addition of such substrate as glucose or other hexose. 3) Regardless of the virulence of bacteria, of all the substrates used, pyruvate and lactate accelerate the reduction most markedly. 4) When pyruvate or lactate is used as a substrate, the rate of reduction by the 6 weeks old cells of virulent strain is markedly decreased compared with that by the 2 weeks old cells, but with avirulent strain the decrease in the rate of reduction is not or hardly noticeable. 5) When succinate is used as a substrate, in the case of 2 weeks old cells, the avirulent strain seems to have somewhat stronger methylene blue reducing activity than the virulent strain. 6) The rate of reduction by the 2 weeks old cells of virulent strain is accelerated when alanine is used as a substrate, but this does not occur in the avirulent strain.