Hydrogen evolution on various Ni-Mo deposits was systematically compared using fractional factorial design (FFD) and response surface methodology (RSM). The electroplating variables such as pH, Ni/Mo atomic ratio and citrate concentration were found to be the key factors affecting the hydrogen evolution activity from the FFD study. The effects of Ni/Mo atomic ratio and citrate concentration in the plating bath on the apparent current density, the exchange current density, and the specific activity (based on i/q*) of hydrogen gas evolution, and on the Mo/(Ni + Mo) ratio of the deposits were examined using regression models. These models, represented as response surface contour plots, showed the maximum hydrogen evolving activity occurring on the Ni-Mo deposit electroplated from the bath with a pH of 8, a Ni/Mo ratio of 3.3 and a citrate concentration of 40 g l(-1), respectively.