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A variety of selective and non-selective reagents [1–18] are used in thin-layer chromatography for identification of amino acids. Such identification is very useful because of the occurrence of the amino acids as the structural units of proteins, in the free state in natural products, and for determination of the C-terminal amino acids of degraded proteins. Of the reagents generally used, ninhydrin, a non-selective reagent, is popular because of its remarkably high sensitivity [2], even though it produces the same purple color with all the amino acids except proline and hydroxyproline. To solve this problem a new reagent, 4-hydroxyacetophenone–isatin-5-sulfonic acid (sodium salt) is proposed. This communication deals with this reagent, which produces distinguishable colors for most of the amino acids. With the proposed reagent detection limits for the amino acids range between 0.1 and 2.0 μg.