THE reaction of 2, 4-dinitro-6-sulphophenyl chloride (DNSP-C1)(Z-chloro-3, 5-dinitrophenyl sulphonic acid) with an amino-acid in the presence of base gives the N-2, 4-dinitro-6- sulphophenylamino-acid (DNSP-amino-acid). A number of these have been prepared and