CrNi austenitic steels and titanium alloy Ti-10V-2Fe-3Al are studied aiming to clarify a reason for difference between two classes of engineering materials in their sensitivity to hydrogen brittleness. Using ab initio calculations, it is found that hydrogen increases density of electron states at the Fermi level in both materials except for its decrease in the titanium alloy at extremely high hydrogen contents. Migration of hydrogen atoms and their interaction with dislocations are studied using mechanical spectroscopy. The enthalpies of hydrogen atoms migration and their binding to dislocations, as well as temperature for condensation of hydrogen clouds around dislocations, are shown to be significantly larger in austenitic steels in comparison with the beta titanium alloy. This is a reason for lower temperature range of hydrogen embrittlement in the titanium alloys. The different hydrogen effect in the studied materials and usage of hydrogen as temporary alloying element increasing plasticity of titanium alloys in the course of their processing are interpreted within the frame of HELP theory. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.