An electron-impact desorption (EID)–flash-filament system incorporating a gas-phase and a surface-ion spectrometer, and a means of vapor-depositing clean surfaces has been used to study the adsorption behavior of hydrogen on polycrystalline nickel surfaces with several surface treatments. The desorption activation energy, coverage, and sticking coefficient varied from 98 kJmole−1,5×1014 molecules cm−2and 0.19, respectively, for freshly deposited nickel films, to 50 kJmole−1,2×1014 molecules cm−2and 0.002, respectively, for nickel foils with no prior cleaning treatment. The results indicate a low number (less than 1% of the surface sites) of active sites for EID ofH3+and a preferential filling of these sites by surface diffusion.