In the fluorescence microscopic study of ascites cells vitally or supravitally stained with acridine orange, which were aspirated from mice, rabbits, rats, cats, doge, monkeys, human, pigeons, and chicken the author obtained the following results. 1. For the vital staining the simple culture method devised in our department is most suitable and as for the concentration of the medium the dilution of 104 is most appropriate. 2. The fluorescence picture by the supravital staining of the ascites cells turned out to be a degenerated picture in vital staining. 3. Active phagocytes have nucleus and cell body stained green and those more active and smaller cells are difficult to be stained and they become stained deep as they degenerate. 4. Ascites phagocytes all possess a series of common characteristics, namely, a peculiar movement pattern, the massing tendency of cytoplasmic granules and nuclei of complicated shape; and these characteristics resemble those of the fluorescence picture of monocytes in blood. Moreover, this similarity tends to be greater in the higher class of animals.