The hydriding/dehydriding rates and the pressure-composition isotherms were measured for LaNi5, LaNi4.85Al0.15 and LaNi4.75Fe0.25 under quasi-isothermal and variable pressure conditions. Isothermal conditions were obtained by reducing the thermal time constant of the experimental device. Empirical rate equations to describe the sorption reaction kinetics were derived. These rates are expressed as a function of temporal composition, saturated composition, temperature, applied pressure and essentially the initial operating conditions which were not considered in most of all the previous studies related to the reaction kinetics of metal hydrides. Besides, the rate equations presented in this work can be integrated easily in the numerical models that predict dynamic flow and heat and mass transfer within realistic metal-hydrogen devices. This paper also discusses the effects of Fe and Al as substituents for Ni on P-C isotherms and reaction rates of LaNi5 alloy. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.