The use of a modified ninhydrin reagent using ascorbic acid instead of potassium cyanide was investigated for the photometric determination of amino acids. It has been found possible to obtain an almost stoichiometric reaction for glutamic acid with a quantitative yield of "Ruhemann's purple", the end-product of the reaction, using ascorbic acid as a safe and economical reducing agent. The modified ninhydrin reagent was composed of 0.5 g of ninhydrin, and 15 mg of ascorbic acid in 60 ml of methyl cellosolve.