An accelerated test for the oxidative discoloration of developed silver images has been studied. While hydrogen peroxide testing has been used to predict the oxidative discoloration of developed silver images in monochrome photographic materials, this method is sometimes impractical when applied to materials stored under a “normal atmosphere” in which the contents of aggressive oxidizing chemicals are small or nonexistant. The article presents a new testing method that uses incubation in an atmosphere of compressed oxygen to accelerate oxidative discoloration. Such incubation for one or two months was found to reproduce the oxidative discoloration occurring in radiographic films stored under a normal atmosphere for four or five years under the climatic conditions of the Tokyo area. And an induction period in which discoloration is imperceptible was observed in the blue density increase of this accelerated testing. From these results, the mechanism of the oxidative discoloration is discussed and the rate-determining process of this discoloration reaction is presumed to be ion migration in the gelatin layer.