1. Of 110 anemic patients observed in the determination of Heinz's body, the patients suffering from aplastic anemia gave the highest value and then those of leukemia, anchylostomiasis, Banti's syndrome, hemorrhagic anemia, essential chlorosis, aglanulocytosis, endocarditis lenta, and Welhoff's disease, in the order mentioned. 2. In the case of the domestic rabbits inoculated with sera of various anemics at the dose of 2cc/kg each, continuously for one week, the order of anemias, if arranged according to the rates of the Heinz-body appearance, will be aplastic anemia, leukemia, anchylostomiasis, Banti's syndrome, essential chlorosis, hemorrhagic anemia, and Welhoff's disease. From this result, practically no substance accelerating the formation of Heinz's body appears to be in the sera of hemorrhagic anemia and Welhoff's disease, while such substances may be thought to exist in the rest of anemic sera (although in the case of essential chlorosis, it is not definitely certain). 3. When the erythrocytes of normal person were left suspended in the sera of various anemics for 3 hours and these erythrocytes measured separately for Heinz's body, the order of diseases arranged according to the rates of the appearance of Heinz's body was more or less like as follows: aplastic anemia, leukemia, anchylostomiasis, Banti's syndrome, essential chlorosis, hemorrhagic anemia, and Welhoff's disease. 4. From these results, it is clear that whether the determination for Heinz's body be made with the blood directly tapped from the patient, or with the domestic rabbits receiving the anemic serum continuously for one week, or with the blood of normal person treated with an anemic serum, in vitro, any one of the three methods proves to be an invaluable aid in differentiation of the anemic patients and in determination of seriousness of the disease itself. Furthermore, it may be assumed that in the sera of the anemics, there exist some subclinic, intrinsic toxins which accelerate the formation of Heinz's body, and that the quantity of such toxins has an important bearing on the estimated values obtained from the blood directly drawn from the patients. Hence in the case of hemorrhagic anemia, the penetrability of Heinz's corpuscles through the wall of erythrocytes should be given an especial consideration. The serum of anemic patient has been found to accelerate the formation of Heinz's body even when made to act directly upon the erythrocytes of the normal persons, in vitro.