A process for the manufacture of indigoid dyes, wherein a functional derivative of the anthranilic acid of the general formula I ##STR1## in which A completes a mono- or polynuclear, substituted or unsubstituted aromatic ring,X represents a hydrogen atom or a protective group for the free amino group which can form an anhydro derivative with the carboxyl group in the ortho-position,Is reacted with nitromethane in the presence of a base or with a salt of nitroacetic acid to give the .omega.-nitro-o-amino-acetophenone derivative of the general formula II ##STR2## in which A and X are as defined in formula I, and this intermediate is condensed by heating with acids to give the indigo compound of the general formula III ##STR3## in which A is as defined in formula I.