In this work the jellium model approach is used to calculate the volume of solution of hydrogen in lanthanum di- and tri-hydrides. Results are compared with the corresponding values of hydrogen diluted in pure lanthanum. Similar behaviors are obtained, which would allow to propose a relation between the volume of solution of hydrogen in pure elements and in hydrides. Within the same approximation, values for the heat of solution are also calculated for the considered systems, and compared with experimental data available in the literature. (C) 2008 Published by Elsevier Ltd. on behalf of International Association for Hydrogen Energy.