It was reported by Weiner, Horie, Sato and others the rise of cold hamaggulutination at the frost-bite times. The author has experiment about the effect of Platonin at the frostbite times, chiefly upon cold hamaggulutination by using rabbits. 1) At the function of the normal reticulo-endothelial system, Platonin has shown to prevent from the cold hamaggulutination; the excited function of the reticulo-endothelial system as well as the increase of γ-Globulin in serum protein has proved. 2) Especially, when the function of reticulo-endothelial system has got down, Platonin has proved to prevent from the rise of cold hamaggulutination and to quicken the function of the said system, along with the increase of γ-Globulin in serum protein. 3) When the function has fallen, Platonin has proved to prevent from the rise of cold hamaggulutination, owing to the experimental refrigeration for the abdomen, along with the decline of the function. 4) As the above results, the author may consider with some significance the close relation between the above said photosensitizing dye, Platonin action, and its remarkable treatment for the frost-bite.