A new silver method was described for the staining of spermatozoa. The method was performed as follows: First, smears of spermatozoa were fixed with 10 per cent formalin and dealt with a dilute gold chloride solution. Then they were impregnated with silver nitrate solution and finally reduced with hydroquinone. The principle of this method is that the middle-piece of the spermatozoa is selectively and distinctly stained in a dark violet tint. Besides, with a slight modification of the original method, the spiral filament in the middle-piece, which was derived from mitochondria and usually is not stained by the ordinary method, may be demonstrated easily. Therefore, it may be said that this method is especially available for the study of fine structure of the middle-piece as well as its general morphology. By using this method, the minute structures of the middle-pieces of spermatozoa of some species were observed and the abnormalities of that portion were demonstrated in photograph.