In order to study some metabolic aspects of Salmonella typhi, the author measured the innert electrode potential of the culture media at 37.5 C with the lapse of time. M/50 phosphate buffer and salt solution were used as the fundamental culture media; glucose, pyruvate, lactate, succinate, malate, glutamate, aspartate and alanine as the substrates; Salmonella typhi 57 S as the test organism. The results were as follows: 1) The most remarkable fall of potential was observed in the media of 10(-3) M glucose, pyruvate and malate, and in 10(-2) M acetate and succinate 2) In the media of lactate or aspartate of the concentration from 10(-1) to 10(-4) M, the potential falled with the decrease of concentration of substrate, while, in that of glutamate, the reverse interrelation was observed. In the media of alanine, no definite interrelation was observed. 3) The lowest potential was below 0 V in the media of glutamate, aspartate and glucose; 0 +100 mV in those of pyruvate, lactate and succinate; +100 +200 mV in those of acetate; +200 +300 mV in that of alanine. 4) When glucose, acetate and glutamate were used as the substrates, the fall of potential was less in phosphate buffer than in salt solution, while, when pyruvate, lactate, succinate, malate, aspartate and alanine were used, the fall of potential was less in salt solution than in phosphate buffer.