Crystal phases of sensitizing specks formed onsulfur+gold sensitization treatment was analyzed by X-ray diffraction. Gold-silver sulfides were formed from silver bromide grains by 1) separate addition of sodium thiosulfate and gold (III) sodium chloride, and 2) addition of gold-thiosulfate complex solution. By greater adding amount of sensitizer to silver bromide, AgAuS was formed. By adding gold-thiosulfate complex solution the product changed from AgAuS toAg3AuS2 with decreasing the mole ratio of sensitizer to silver bromide. Ag2 S was not observed in any case. This suggests that thesulfur+gold sensitization speck is homogeneous and consists of one component, that isAg3AuS2, or the mole ratio of gold and sulfur in sensitizing speck is1: 2.