The author conducted a series of experiments on Barkan's easily-splitoff iron E and E' and obtained the following results. 1. There are distinct differences between the inhibtory action of carbor mcnoxide and that of inactivated gas on choleglobin liberating iron. 2. In the estimation of E and E' in ten abult males, the average sum of E and E' has been found to be 1.52 mg%, with E' being 0.34 mg%, and E occupies 77.33 per cent of the total. This value is somewhat higher than that of Barkan. 3. In the study of various conditions of reagent, governing the reaction, when the reaction is made to take place at 0°C without any supply of oxygen, it is retarded most markedly, but it is not completely stopped. 4. In the reagent the decomposition progresses from hemoglobin to E and E' but an exact quantitative analysis has been difficult.