Amount of photolytically separated silver in silver chloride emulsions containing and not containing dye (3, 3'-diethylthiatricarbocarbocyanine iodide) has been determined by the differential potentiometric titration method and it was found that the dye actually desensitized the photolysis of silver chloride. The number of silver atoms desensitized per molecule of the dye can be larger than 6, and this suggests that the dye or the dye aggregate can act repeatedly in desensitization.