solution of nitrothiosulfobenzoate  was diluted 10-fold and a chromatogram was sprayed with it. Cysteine and cystine gave yellow spots on a white background. When silica gel or polyamide is used as the support, 2 ~g of cystine can be detected in a spot, while when paper is used the amount is ~ i0 pg. Cysteine appears rapidly. In the case of cystine, the coloration develops in 10-15 min. Other amino acids are not revealed by this reagent.