Following the evidences advanced in a previous paper that metabolic gases are concerned in the production of growth-oxidation-reduction potentials observed in cultures of bacteria, experiments have been arranged to test the effects of such gases in comparison with other factors. Growth and oxidation-reduction potentials have been determined simultaneously in anaërobic buffered broth cultures of Es. coli. It is shown that in sugar-free broth there is a sudden fall in potential at the beginning of the logarithmic growth period. The addition of glucose to the medium was found to induce an earlier and more precipitous fall in potential which is coincident with the first evolution of gas. At the same time there was found to be evidence of a non-gaseous electromotively active system in these cultures.