The hydrogen evolution reaction has been investigated on sodium-tungsten bronzes (Na,WO,) of various stoichiometrles (0.34 < Y < 0.89) in sulfuric acid solutions. Steady-state current-potential relationships and capacity-potential profiles were examined The fil-si cathodic skady-stale currenpotential curve in the ascending direction indicates the presence of two distinct Tafel lines with slopes ofabout -2RT/F and -RT/2F. This behavior is interpreted in termsof alternative reactions. At low overvoltages the mechanism is fast discharge-slow clcctrochcmical desorption. while at higher overvoltagcs a fast discharge-slow recombination mechanism is indicated. The change of the rate-determining step from one potential range to the other is attributed to a change in the crystallographic structure of the electrode surface, eg, a lattice dimensional change of the hydrogen tungsten bronze. The Tafel slope for an electrode pre-polarized cathodically is close lo -RT/F. In this case the rate-determining step is proposed to be the surface diffusion of adsorbed hydrogen atoms to recombination sites. The u-value in Na,WO, and the platinum content of the electrode were found to have no significant effect on the rate of the hydrogen evolution reaction.