Mechanically alloyed Mg2Ni/Ni nano-composite and Zr55Cu30Ni5Al10 amorphous powders were hydrogen charged at constant pressure under ball milling. While the Mg-based samples were able to absorb large amount of hydrogen under static conditions, and from the very onset of the mechanical treatment, an incubation milling period was needed for the hydrogen activation in the case of the amorphous sample. A progressively decreasing rate characterizes the process kinetics in the case Of Mg2Ni/Ni, whereas a self increasing sigmoid trend was observed for the multicomponent Zr alloy, which showed structural demixing phenomena in the absorption course. Irrespective of the system, the maximum absorption rate was strongly dependent on the milling intensity (Watt . g(-1)). The hydriding rate (mole . g(-1)s(-1)) and the mechanochemical yield (mole . Joule(-1)) were used to compare the processes on an absolute scale. In the case of Mg-based alloy, comparison was also made between mechanically induced and thermally (static) activated hydriding processes. Attempt was also made to work out the hydrogen atoms absorbed at the ball-hit event. (C) 2004 Kluwer Academic Publishers.