The mechanisms of formation of the surface layer of lead silicate glasses during their interaction with hydrogen under heating were studied by X-ray photoelectron spectroscopy. The thermostimulated change in the composition of an outer surface layer (with a thickness in the order of 100 Angstrom) goes in the direction of the minima in the liquidus line of the diagram of states for Pb0-SiO2, The reduction process follows the scheme [PbO3](delta-) --> Pb-mod - O --> [PbP](ion)--> Pb-o, where [PbO3](delta-) is the network-forming lead (glass former), Pb-mod the modifier lead, [PbO](ion) the intermediate lead-oxygen compound with a more ionic character of the Pb-O bond. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.