Hydrogen absorption in two LaNi5-H2 reactors is experimentally and theoretically investigated. In the experimental program, two tanks are filled with LaNi5 alloy and hydrogen is charged with a constant pressure. The temperature changes in the tanks are measured at several locations and recorded in a computer. Hydriding process is identified from measured temperature histories. In the theoretical program, a two-dimensional mathematical model, which considers complex heat and mass transfer and fluid flow is developed and numerically solved. The numerical results are compared with the measured data to validate the mathematical model. A reasonable agreement between the numerical results and experimental data is obtained. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.