A water-soluble azo compound of formula ##STR23## in which Y is vinyl or --CH.sub.2 --CH.sub.2 --Z in which Z is chlorine, bromine, fluorine, lower alkanoyloxy, benzoyloxy, sulfobenzoyloxy, benzenesulfonyloxy, toluenesulfonyloxy, lower alkylsulfonylamino, arylsulfonylamino, phenoxy, dialkylamino, each alkyl being of from 1 to 4 carbon atoms, thiosulfato, phosphato or sulfato;
- n is the number of zero or 1;
- D is phenylene unsubstituted or substituted by one or two substituents selected from the group consisting of lower alkyl, lower alkoxy, hydroxy, lower alkanoylamino, chlorine, bromine, fluorine and carboxy;
- by one nitro substituent;
- by one substituent of the formula Y--SO.sub.2 --(CH.sub.2).sub.n -- in which n is 1;
- by a plurality of substituents selected from the group consisting of said one or two substituents, said one nitro substituent and said one substituent of the formula Y--SO.sub.2 --(CH.sub.2).sub.n --;
- or
- the benzothiazol-2-yl radical in which the group Y--SO.sub.2 --(CH.sub.2).sub.n -- is bonded to its carbocyclic ring, or said radical in which the benzene ring is additionally substituted by lower alkyl, lower alkoxy, hydroxy, lower alkanoylamino, nitro, chlorine, bromine or sulfo;
- R.sup.1 is hydrogen, lower alkyl, lower alkenyl, lower alkyl substituted by phenyl or hydroxy or by both, lower alkyl substituted by phenyl which is substituted by substituents selected from the group consisting of methyl, methoxy and chlorine, or by said substituted phenyl and hydroxy, or is alkyl of 2 to 4 carbon atoms substituted by acetoxy, propionyloxy or phenylsulfonyloxy or by cyano, or is alkyl of 1 to 4 carbon atoms substituted by carboxy or carbonamido or carbalkoxy of from 1 to 4 carbon atoms in the alkyl moiety, or is halogenoalkyl of 2 or 3 carbon atoms or is lower halogenoalkenyl, or is a group of the formula --A--SO.sub.3 M;
- A is ethylene, or propylene of the formula ##STR24## in which X is hydroxy, acetoxy, propionyloxy or phenylsulfonyloxy or is a halogen;
- R.sup.2 is hydrogen, lower alkyl, lower akloxy unsubstituted or substituted by hydroxy, acetoxy, carboxy, carbamoyl, cyano or halogen, or is halogen or trifluormethyl;
- R.sup.3 is hydrogen, lower alkyl, lower alkoxy unsubstituted or substituted by hydroxy, acetoxy, carboxy, carbamoyl, cyano or halogen, or is halogen;
- M is hydrogen or an alkali metal.