In polargraphy, bacterial cell revealed two special phenomena; e. g. maximalization of electro-reduction potentials and adsorption of cobalt ions. The former phenomena has been less known until to date. Inteding to know the relation between this phenomena and surface structure of the bacterial cell, the author found a simple method to express accurately with inhibitory of electro-reduction potential. In hibitory activity was strkingly higher in gram negative bacterial cell than that in gram positive. and a little higher in S-type than in R-type. This tendency was completely identical with that of surface binding water which measures by dielectric spectrometory as previously reported. Same evidence was also found in the process of production of adaptation enzyme. Thus inhibitory activity of eIectro-reduction potentials was presumably due to increased binding water on the surface area of bacterial cell. On the other hand, inhibitory activity of electro-reduction potential exactly reflexed the speciality in immunological phenomena in which antigen complex was being polysaccharide-polypeptide-lipid compound. Individual kind of bacterial cell has proven to show special crossing effect in the cobalt-protein wave. As the crossing point of electro-reduction curve showed parallel tendencies with polypeptide activity on the surface of bacterial cell during process of production of adaptation enzyme, growth of the cell etc, polarography has been an effective tool to demonstrate physiolo-chemical state of bacterial surface.