Investigations of LaNi5 by means of photoemission spectroscopy, Auger electron spectroscopy and measurements' of the magnetic susceptibility and magnetization show that in a surface layer La diffuses to the surface and metallic Ni precipitations are formed. This surface segregation is enhanced by the presence of oxygen. The segregation continues with each cycle of hydrogenation. This represents a self restoring mechanism of the active surface, since the highly reactive La oxidizes and keeps the Ni metallic. Dissociative adsorption of H2 then occurs at the Ni precipitations. © 1979.