The hydrogen evolution reaction (HER) on RuO2 coated nickel electrodes was investigated by d.c. polarization studies and a.c. impedance measurements in alkaline solution. The electroactive RuO2 coatings were prepared by thermal decomposition of a RuCl3 solution at 450 degrees C in air. The real surface area of the cathodes was estimated from cyclic voltammetric measurements and from the double layer capacitance (evaluated by impedance measurements). A mechanism for the HER has been proposed involving two steps (Volmer and Heyrovsky reactions). The rate constants of the forward and backward reactions of these two steps have been estimated by a nonlinear fitting procedure.