The kinetics of bleaching reduction of developed silver image was studied in order to understand the differences between reduction by a subtractive reducer and reduction by a proportional reducer. It was shown that the alteration in the contrast of a negative after reduction depended on the rate of the bleaching and also on the situations of silver particles in the developed emulsion layer. If the rate limiting step in the reaction is diffusion of bleaching agent in the layer, the rate is proportional to a half power of silver concentration (silver contents per unit volume of the layer). On the other hand, if the step is activation of the reaction, the rate is inversely proportionai to the radius of the silver particle. A ferricyanide-hypo reducer (pH 6.1), of which bleaching rate is diffusion controlled, acts as a subtractive one because the silver concentration is constant regardless of the exposure level. An ammonium persulfate reducer (pH 3.2), of which bleaching rate is determined by activation, acts as a superproportional one because the silver particle size in the highlight is smaller than that in the shadow.