The anodic currents of the superadditive mixtures of N, N-diethyl- p -phenylene diamine (DEPA) and ascorbic acid (AA) were remarkably greater than the sum of the individual currents on the gelatin coated silver electrode and had a good correlation with the superadditivity of development. Both the rate of development ane the anodic current at a working potential of silver specks at development were proportional to the concentration of DEPA when AA was large excess, and the rate of the anodic reaction of DEPA was much faster than that of AA. These findings support the catalytic current mechanism of the superadditivity that the anodic reaction of a main developing agent is catalytically amplified by an auxiliary developing agent, the mechanism being valid in the cases of the mixtures such as Phenidone-hydroquinone, Metol-hydroquinone, Phenidone-AA and Metol-AA, as reported in previous papar. It was concluded that the difference of the superadditive effects between DEPA and Phenidone was not due to the difference in the regeneration rates of the auxiliary agents by the main agent but due to the difference in the half wave potentials of the two.