When Y(III) is added into an aqueous solution, the mechanism of the cathodic process on steel is deeply modified, compared to the mechanism in uninhibited solutions. In air-saturated solutions, the potentiodynamic cathodic curves present three distinct zones: a short current plateau due to oxygen reduction, then a straight current increase with a slope value close to 0.12 V dec(-1). Finally, at still more negative potentials, the cathodic reaction becomes once again diffusion-limited. In the present work, the mechanism of the cathodic process is discussed from potentiodynamic experiments performed in 0.5 M sodium chloride solutions, under different hydrodynamic conditions using a rotating steel disk electrode, and as a function of the concentration of Y(III) in the solution. In addition, an electrochemical microbalance coated with gold, with or without a steel overlayer, was used to follow the mass increase due to Y(III) hydroxide precipitation, in the three parts of the cathodic range. It clearly appears that in the presence of Y(III) in the solution, the overpotential for the reduction of water bounded to yttrium in the Y(III) aqua-complex is strongly decreased at a potential close to the equilibrium potential for water reduction. (c) 2006 The Electrochemical Society.