We have carried out electrochemical, sensitometric, and electron microscope investigations of the reactions of the photosensitive phase of a thermally developable photomaterial. We have found that formation of icrocrystals of silver bromide by metathetical reaction of silver stearate with bromide in aqueous solution leads to precipitation of silver bromide as a separate phase, accompanied by dissolution of silver stearate microcrystals. The size of the AgBr microcrystals increases with increasing concentration of the brominating agent, but does not exceed 0.07 μm. Latent image centers formed by the AgBr microcrystals are capable of catalyzing thermal development if the microcrystals have been formed in the presence of the carboxylate. The process of thermal amplification of the latent image centers may, however, be achieved on AgBr crystals having no physical contact with silver stearate. We propose that thermal development of latent image centers on AgBr crystals proceeds by diffusion of silver stearate-derived “droplets” to the development centers. Fog formation, on the other hand, nucleates independently of the AgBr microcrystals.