Azo dyes of the formula (1) ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 independently of one another are each hydrogen or substituted or unsubstituted C.sub.1 -C.sub.4 alkyl,R.sub.5, R.sub.6, R.sub.7 and R.sub.8 independently of one another are each hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, halogen or sulfo,D.sub.1 and D.sub.2 independently of one another are each a radical of the benzene or naphthalene series, andY.sub.1 and Y.sub.2 independently of one another are each halogen, substituted or unsubstituted amino, morpholino or piperidin-1-yl or are piperazin-1-yl which is unsubstituted or substituted on the nitrogen,with the proviso that D.sub.1 and D.sub.2 are not both sulfophenyl if Y.sub.1 and Y.sub.2 are chlorine and R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are hydrogen, are dyes for various substrates, especially cellulosic fibre materials.They are stable to high temperatures and are therefore particularly suitable for the one-bath, single-stage dyeing of polyester/cotton blend fabrics with a disperse dye of the polyester fibres under the dyeing conditions for polyester fibres.