The compounds RENi4Mg have been elaborated by mechanical alloying (MA) and a subsequent heat treatment at 600 degrees C for 1 h. The lattice parameters are in good agreement with those already reported: 7.165 angstrom for LaNi4Mg, 7.030 angstrom for CeNi4Mg and 7.038 angstrom for GdNi4Mg. The hydrogen sorption behaviors are strongly influenced by the rare earth used: for La compound, hydrogen absorption leads to a structural change and no desorption can be observed, for Ce compound, no reaction towards hydrogen can be noticed and for Gd compound, hydrogen can be absorbed and desorbed reversibly at room temperature. Moreover, for GdNi4Mg, no structural change is reported after hydrogenation and only a slight volume expansion can be noticed (e.g. 5%). The MA process has also been used successfully for the elaboration of GdNi4-xAlxMg up to x = 1. In these substituted compounds, hydrogen can also be absorbed and desorbed reversibly at room temperature. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.