In the study of reaction kinetics between hydrogen and hydriding alloys, what is the most important is to obtain intrinsic kinetic data. The hydriding kinetics of 0.5 g La1.5Ni0.5Mg17 sample in the two-phase (alpha-beta) region was investigated as a function of temperature and pressure in the ranges 553-573 K and 0.256-0.992 MPa H-2 respectively. Mathematical analyses of the time-dependent hydrogen absorption curves indicate agreement with Jander diffusion model, [1 - (1 - xi)(1/3)](2) = k(T, P)t, which suggests that the rate-controlling step for hydrogen absorption is three-dimensional diffusion. An apparent activation energy for such diffusion process of 83 +/- 1 kJ/mol H-2 has been obtained from the absorption data. (C) 2004 Kluwer Academic Publishers.