The mechanism of the fog inhibiting action of organic antifoggants in development process is discussed by considering the probability of their adsorption on fog or latent image centers. The probability that every fog center on a grain is covered by antifoggant molecules, and therefore the grain becomes undevelopable, is larger than that every latent image center on a grain is covered by them, because the number of fog centers on a grain is less than that of latent image centers on a grain.