In this work, a study is presented that shows the evolution of the valence band analysis of NaAlH(4) doped with 1 mol% of Ce- and 3 mol% of Ti/Zr-hydride using X-ray photoelectron spectroscopy (XPS). The two NaAlH(4) + metal hydride systems contained ball-milled, dehydrogenated, and rehydrogenated samples. The density of states of NaAlH(4), Al, and Na(3)AlH(6) were calculated with the generalized gradient approximation (GGA). in both of the two-system samples, during the dehydrogenation and rehydrogenation, most electrons in the p orbital disappeared, and the electrons in the s orbital increased. The catalyst Ce-hydride activated the electrons in the s orbital, whereas Ti/Zr-hydride affected those of the p orbital. Thus, the dehydrogenation and rehydrogenation might activate the more electrons in the Al s and p orbitals. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.