The results of a systematic investigation of the effects of microstructure/substructure on the secondary creep behaviour of alpha(2)-based titanium aluminide alloys are presented. This includes a study of the effects of heat treatment on the steady-state creep behaviour of alpha(2) + beta-processed Ti-24Al-1 1Nb and Ti-25Al-1ON b-3V-1Mo at 540, 650 and 760 degrees C, and an investigation of the effects of creep deformation on dislocation substructures in Ti-24Al-11Nb. The parameters that control secondary creep deformation are identified for both alloys, and the results are compared with data obtained for conventional high-temperature near-alpha titanium alloys and beta-forged Ti-24Al-10Nb-3V-1Mo.