The effect of additives on the hydrogen absorption-desorption properties of three series of composites (i) 85% Mg-15% Mg2Ni1-xMex (Me= Fe, Co; x = 0, 0.1, 0.3); (ii) 75% Mg-15% Mg2Ni-10% V and 75% Mg-15% Mg2Ni-10% C and (iii) 90% Mg2Ni-10% V and 90% Mg2Ni-10% C obtained by mechanical alloying in different atmospheres was studied. The Mg2Ni1-xMex, vanadium and graphite additives were found to have a positive effect on the hydriding kinetics of magnesium, especially favorable due to the presence of cobalt in the composites 85% Mg-15% Mg2Ni1-xCox which preserved a high-absorption capacity with decreasing temperature (4 wt% H-2 at a hydriding temperature of 423 K). With 90% Mg2Ni-10% V (C) composites, the additive showed an analogous positive effect on the hydriding kinetics and absorption capacity as compared with that of pure Mg2Ni. The role of the milling atmosphere (argon or hydrogen), with respect to the absorption-desorption characteristics of these composites was also studied. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.