The process of hydrogen embrittlement of metals in the area of threefold junctions of grain boundaries at the expense of molecular hydrogen pressure in the voids and as a result of hydride-phase formation has been considered. The physical base of these mechanisms is diffusion migration of hydrogen atoms in the stress fields of structural imperfections. The threefold junctions of grain boundaries, which stress field is simulated by wedge disclination, are considered as the main structural imperfections. The exact analytical solution of a diffusion equation in the stress fields of the wedge disclination hat; been obtained. The analytical dependencies for the molecular hydrogen pressure in the voids near the threefold junctions of grain boundaries have been given. This pressure favors opening the microcracks along the grain boundaries. Hydrogen embrittlement of metals has been observed in the macroscopic scale. Kinetics of hydride-phase formation in the area of the threefold junctions of grain boundaries has been studied. The considerable volumetric changes of hydride in comparison with the basic metal lead to the void formation along the interphase boundaries. The results of a theoretical analysis are used for explaining the hydrogen embrittlement of metals within a wide temperature range. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.