The invention relates to a process for the preparation of azo dyes of the formula ##STR1## or mixtures thereof, in which Ar is a substituted or unsubstituted phenyl, naphthyl or aromatic heterocyclic radical and Y is a group of the formula --O--R, --S--R or ##STR2## in which R is a substituted or unsubstituted alkyl, aryl or heterocyclic radical and R.sub.1 and R.sub.2 independently of one another are hydrogen or a substituted or unsubstituted alkyl, aryl or heterocyclic radical, and the groups R.sub.1 and R.sub.2, together with the nitrogen atom to which they are bonded, can form a ring.The process comprises first coupling dimeric malonodinitrile with a diazo component and cyclizing the resulting intermediate with an alcohol, thioalcohol or amine.