A method is described for the determination of the potential of any organic oxidation‐reduction system within the range of applicability of the dropping mercury electrode and from a single polarographic curve. No matter whether the system is in a completely oxidized or in a completely reduced form, the half‐wave potential will give the theoretical, E′o. Furthermore, the approximate concentration of the system and the ratio of oxidant to reductant may be read from the same curve. On the basis of a series of curves for different pH values, an insight into the actual electrode process is obtained and an intimation as to the structural characteristics of the reactants. Furthermore, the existence of semiquinones is graphically demonstrated and the E1 and E2 potentials characterizing the two steps in their oxidation are determined.