The invention comprises basic dyes of formula wherein R1 is hydrogen or a C1-C8 alkyl group, R2 is a methyl or ethyl group, R3 is a chlorine or bromine atom, or cyano or C1-C8 alkyl-sulphonyl group, R4 is a hydrogen, chlorine or bromine atom and Z is a C1-C3 alkylene or -CHOH.CH2-group. The dyes are prepared by diazotizing an amine of formula and coupling the diazonium compound with a compound of formula The dyes are preferably used to colour articles made from polymers composed of more than 80% acrylonitrile in red, blue or brown shades.