Abstract: Disclosed is mass-dyed linear, saturated, aromatic polyester comprising, as dyestuff, a compound or mixture of compounds selected from those of formulae I and II, ##STR1## wherein R.sub.1 is a radical of formula ##STR2## R.sub.2 is hydrogen or a radical of formula ##STR3## of R.sub.3 and R.sub.3 ', both are hydrogen, or one is hydrogen and the other chlorine or bromine, or both are chlorine or bromine,R.sub.5 is hydrogen, chlorine, bromine or methyl,R.sub.5 ' is hydrogen, chlorine, bromine, nitro or a 4-phenyl, 4-chlorophenyl, 4-bromophenyl or 4-para-nitrophenyl group,R.sub.6 is hydrogen, chlorine or bromineR.sub.6 ' is hydrogen, chlorine, bromine or methyl, andR.sub.7 and R.sub.9 are the same and are chlorine or bromine,With the provisos(i) R.sub.2 is hydrogen when R.sub.1 is a radical (1) or (2) or when R.sub.1 is a radical (3), in which R.sub.5 is phenyl or chloro-, bromo- or nitro-phenyl,(ii) R.sub.3 and R.sub.3 ' are both hydrogen when R.sub.1 is a radical (1), (3) or (4),(iii) R.sub.