The dynamics of hydrogen release from metals to the closed volume at a fixed temperature is studied. The surface lag-time of hydrogen depending on both the reaction of association of hydrogen atoms into a molecule and the presence of impurity barriers at the surface is taken into account by means of introduced coefficient of boundary permeability. It has been shown that the time dependence of hydrogen pressure is characterized by three stages. These are the linear stage, the square-root stage and the approaching of equilibrium according to the exponential law. The model allows to reveal the predominant mechanism influencing hydrogen release on the base of the form of the kinetic curve. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.