Abstract: The photo-induced ESR signal intensity at g=2.0023 of dye-containing silver bromide model emulsions was found to increase parallel to the light sensitivity with increasing chemical ripening time, as opposed to an earlier indication in the literature referring to some practically used emulsions(4). This discrepancy is interpreted by supposing a dual role of the sensitization product, which can act in the process of latent image formation both as electron trap and as hole trap. In a model emulsion as used in the present work, the silver halide grains represent, before chemical sensitization, a highly regular structure in which electron traps do not exist to any considerable extent, and hence the hole traps dominate because of the presence of adsorbed gelatin as a halogen acceptor. Under these circumstances, as the chemical ripening process proceeds, the sensitization product, though a "dual" trap, should lead to an increase in the concentration of electron traps relative to that of hole traps. This will prevent electrons from recombining with positive holes. The latter can then freely interact with dye molecules adsorbed on the grains to form dye free radicals which are believed to be responsible for the photo-induced ESE signal of the emulsion. If, on the contrary, electron traps axe preponderant in the primitive emulsion, as might be the case with most of practically used emulsions, the increase in hole trap concentration during chemical ripening will become more important than that in electron trap concentration, and will thus invoke a decrease in photo-induced ESR signal intensity.