Aminothiazoles, benzothiazoles, thiadiazoles and thiophenes were diazotised and coupled to N‐β‐cyanoethyl‐N‐β‐hydroxyethylaniline to give dyes which coloured polyester in orange to blue hues. The colour of the dyes is discussed with respect to the nature of the heterocyclic ring and substituents therein. Solvent effects on the visible absorption maxima of some of the dyes are also reported.