Halogenobenzothiazolylazo dyes were prepared by coupling diazotised halogeno‐2‐aminobenzothiazoles toN‐β‐hydroxyethyl‐N‐β‐cyanoethyl‐m‐toluidine. The colour and fastness properties of the dyes on secondary cellulose acetate and on polyester fibre are compared with respect to the position and the nature of the halogen atom. Dyes containing 4‐halogeno atoms have the highest fastness to sublimation on polyester fibres; the fastness to light of the dyes is considerably higher on secondary cellulose acetate than on polyester fibres, but differences between indi