X-ray diffraction (XRD) analysis revealed that nanocrystalline Ti hydride(s) was in situ formed during mechanical milling 1:1 NaH/AI mixture with metallic Ti powder. The composition of the formed Ti hydrides varies slightly upon changing the milling atmosphere from inert Ar to reactive H-2. Directly doping sodium alanate with commercial Ti hydride was found to result in similar dehydriding kinetics, hydrogen capacity, and cycling stability to those of the samples doped with metallic Ti. Moreover, according to the XRD results, the Ti hydride(s) remains stable in the de-/hydrogenation cycles. On the basis of these results, a discussion regarding the nature of catalytically active species was given. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.