Abstract: An azo compound that is free from sulphonic acid groups of the formula ##STR1## in which D represents the radical of a diazo component, A represents an optionally substituted, 1,4-phenylene radical, R.sub.1 represents an optionally substituted alkyl radical, R.sub.2 represents an optionally substituted alkylene radical, Alk represents an alkylene radical of 1-4 carbon atoms and Y represents an imino group, a sulphur atom or an oxygen atom and ring B may be substituted by bromine, fluorine, chlorine atoms, cyano, nitro, trifluoromethyl, alkyl, alkoxy, acylamino, acyloxy, carbalkoxy, optionally N-alkylated carbamoyl and optionally N-alkylated sulphamoyl groups and by a benzo residue. The compounds dye polyester fibres in yellow, red or blue shades with good fastness.