1. The author showed by means of paper-electrophoresis using o-nitrosoresorcinmonomethylether (hereafter N. R. M. E.), a colourdeveloping reagent, that iron in serum combines with β-fraction of serum protein. 2. The author proposed a new method for the determination of serum iron by means of paper-chromatography. Procedure is as follows. In a centriguged tube, 0.5 ml. of clear serum is taken, acidified with 0.15 ml. of 20% HNO(3), and allowed to stand for 20 minutes. After addition of 0.2 ml. of saturated solution of CH(3)COONa and 1 ml. of acetic acid-sodium acetate buffer solution (pH: 3.8), the mixture is kept for at least 10 min. and filtered through Toyo-filter-paper No.5 A. The clear filtrate is taken in a stoppered test tube (the inside diameter: 1.2 cm.; height: 15 cm.). To this filtrate are added 0.2 ml. of 20% Hydroxylamine hydrochloride and 0.25 ml. of saturated aqueous solution of N. R. M. E. After being allowed to stand for at least 20 min., the mixture is shaken with 5 ml. of carbon tebrachloride. Then the excess of N. R. M. E. is removed. The supernatant aqueous solution (0.2 ml.) is used for a determination sample. The sample is placed on the paper (Toyo,filter-paper No.51 or 50) in a thin line at a distance of 10 cm. from the edge, and the spots are developed with 90 % ethylalcohol. After development for 4-6 hours, a green-coloured linear spot appsars at a distance of 12-16 cm. from the origin-point. Spot intensity at 670 mμ is measured with Natsume's densitometer, and from this, concentration of Fe can be estimat.ed on the standard graph (Fig. 5). 3, Effects of radioactive thermal spring bathing and internal use of vitriol water upon serum iron levels were studied with the result.s as follows. The above-mentioned author's method of determining the iron level in a small amount of serum is very convenient in investigating iron metabolism in the field of balneotherapy. The author examined changes of iron levels in serum after radioactive thermal bathing as well as after internal use of acid vitriol water. a) The iron levels in serum were maasurecl by the author's method before and 5, 30 and 60 minutes after the radioactive thermal bath (Rn-content: 10-30 Mache, 42-3°C., for 10 min,). The iron levels in the serum of healthy subjects showed no significant change after the thermal bathing. b) Yanahara Mineral Water (an acid vitriol water, pH; 2.2) contains 0.045 gm. of Cl(-), 12.35 gm. of SO(4)(--), 2.5 gm. of Fe(++)+Fe(+++), 0.0938 gm. of Al(+++) and 0.0001 gm. of Cobalt in one liter. i) Thirty ml. of Yanahara, water diluted with plain water to 200 ml. (Fe(++) content: ca. 75 mg.) and administered to health fasting subjects orally. As a control matter, 0.65 gm. of Glukon-F powder (Fe(++) content.: ca. 75 mg.) was then given. Blood samples were taken from the cubital vein before and 1, 3 and 6 hours after the intake of the dtriol water. Iron contents of the serum samples were measured by the author's paper chromatographic method. The results were shown in the table and the figure. The iron contents of the serum after the intake of the mineral water were higher than in the case of the control. ii) Two ml. of Yanahara vitriol water was administered to rabbits with the aid of a stomach tube, and serum iron levels wera determined before and 1, 3, 4 and 6 hours after the administration. An amount of 0.05 gm. of Glukon-F powder was dissolved in 5 ml. of plain water, and this solution was given to rabbits as a control. After the internal use of vitriol water, iron levels in serum rose and remained unexpactedly high for about 1-4 hours, in a manner that did not. correspond to the amount of iron in the given mineral water. So that it was suspected that the iron originally contained in the living subjects had been mobilized by the intake of vitriol water. Iron levels in serum after administration of a solution of Glukon-F powder were lower than in the case of the mineral water.