A series of new heterocyclic disperse dyes were prepared by diazotising 11H-7-amino-2-chloro-isoindolo[2,1-a]benzimidazole-11-one and coupling with various mono- and di-N-substituted aniline derivatives. The resultant dyes were characterised using standard spectroscopic methods and their dyeing performance on nylon 66 and polyester fabrics was assessed. Results of the latter studies indicated that dye bath exhaustion was moderate to good and the dyed fabrics had good to very good fastness properties.