A method of forming a color diffusion transfer image by heat development is disclosed. This method comprises effecting imagewise exposure of a thermally developable photosensitive material containing an organosilver salt and a thermally non-diffusing color providing material capable of releasing a chelatable diffusing dye upon heat development, thermally developing the exposed photosensitive material to form an imagewise pattern of the chelatable dye from said color providing material, and diffusing and transferring at least part of said imagewise pattern into an image-receiving layer containing a polyvalent metallic ion that is superimposed on the photosensitive material, thereby forming on the image-receiving layer an imagewise pattern of the dye that has chelated with the polyvalent metallic ion.