Azo dyestuffs of the formula ##STR1## wherein R.sub.1 denotes acyl,R.sub.2 denotes hydrogen, fluorine, chlorine or trifluoromethyl,R.sub.3 denotes hydrogen, optionally substituted C.sub.1 -C.sub.4 -alkyl, cyclohexyl or optionally substituted phenyl andR.sub.4 denotes hydrogen or C.sub.1 -C.sub.4 -alkyl groupare suitable for dyeing natural and synthetic fibre materials, for example for dyeing wool or polyamide fibres, in level read to violet shades with very good fastnesses to light, wet processing and perspiration, the color yield being good.