In Ti-22Al-27Nb, the beta-gamma hydride transformation which is a bcc-->bct transition in crystal structure exhibits some of the characteristics that are considered typical of martensitic transformation. We investigated surface relief and microstructure of a pre-deformed beta(0)(132) single-phase specimen hydrogenated to different hydrogen contents. When P hydride is formed, no distinctive changes are found on their electro-poli shed surfaces. However, surface relief with a thin plate-like morphology is found after the beta-gamma hydride transition. The plates contain a high density of aligned striations which are determined to be <111> screw dislocations. Crystallographic features of the beta-->gamma hydride transformation analyzed by the Bowles-Mackenzie method agree well with the experimental observation. The role of aligned dislocations in improving the hydrogen absorption/desorption properties of Ti-22Al-27Nb is discussed based on a discovery of the similarities between the strain around <111> screw dislocations and that induced by the formation of hydrides. Possible ways to control the hydrogen absorption/desorption properties via defects engineering are proposed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.