[en] The interaction of radioactive cobalt with amino acids such as glycin, alanine and aspartic acid which are relatively abundant in sea water was experimentally studied regarding the adsorption on chelate-producing resin and the solvent extraction. The artificial sea water was prepared according to Lyman and Fleming's prescription, and it contains 19.00% chlorine. The natural sea water contains 18.27% or 18.44% chlorine. The filtrate of chlorella culture water was prepared by adding 0.01% aluminum sulfate, 0.0015% of calcium super phosphate and 0.0005% of urea to the artificial sea water, cultivating Chlorella for three weeks in the water, and then filtering in case of the fresh cultivation filtrate. The water was reserved in a cold and dark place for three months after culture and filtered in case of reserved cultivation filtrate. One ml of chelate-producing resin was added to 5 ml of the water containing the known amount of Co-60, and the adsorption on the resin was studied by the batch method. The solvent extraction was performed by the dithizone in carbon tetrachloride method and the 2-nitroso-naphthol in chloroform method. The radioactivity of Co-60 gamma-ray was measured with the automatic scintillation countor. The experiments revealed that (1) both the adsorption and the solvent extraction of cobalt in the presence of amino acids are prevented, and it is believed that the organic cobalt with cobalt ions being masked is produced; (2) the reaction of producing such organic cobalt containing amino acids is slow and takes 20 days or more to reach equilibrium stage at room temperature; and (3) the production of the organic cobalt differs among amino acids. (Iwakiri, K.)