Aqueous solutions of sodium salts of .alpha.-aminocarboxylic acids practically free of foreign salts are produced by saponifying the corresponding hydantoin at a temperature between 110.degree. C. and 180.degree. C. with a mixture, in each case based on the hydantoin, of 1 equivalent of sodium hydroxide and 2 equivalents of calcium oxide or hydroxide, separating off the precipitated calcium carbonate after the end of the saponification and concentrating the aqueous sodium salt solution remaining to drive off the ammonia contained therein.