The effects of quaternary salts on the development by N, N-diethyl- p -phenylenediamine (DEPA) developer and hydroquinone (HQ) developer were studied on the basis of the electrochemical model of development. The effects of dodecylpyridinium chloride (DPC) on the rate of development were good agreement with those on the anodic current of the developer at a gelatin coated silver electrode. Quaternary salt adsorbed on development center changes the structure of the electric double layer and shields in part the effective surface for the anodic reaction of the developer. The acceleration by DPC at the higher concentration in HQ developer can be ascribed to the elimination of the restraining action of gelatin, accompanied with the micell formation. The strong inhibition at the lower concentration may be caused by the intensification of the inhibitory actions of bromide and sulfite ions, by coadsorption on the development center. On the other hand, no elimination and intensification appear in DEPA developer, because gelatin and these ions do not affect substantially on the anodic reaction of the developer. It was suggested that the charge barrier effect did not need for the explanation of the effects of quaternary salts.