Cathodic reduction of nitrate ions at a polycrystalline silver electrode was reexamined, particularly, in the presence of La3+ and Al3+ cations in the solution. Although the onset potential for this reaction is located above the zero charge potential of Ag, a marked catalytic effect of La3+ ions, was observed, resulting in a large positive shift of the voltammetric peak associated with nitrate reduction. Electrochemical quartz crystal microbalance measurements demonstrated formation at the electrode surface, close to the onset potential for NO3-reduction, of films assigned to La(OH)(3) and/or Al(OH)(3) in the solutions containing La3+ and Al3+ ions, respectively. The observed effect of La3+ ions upon nitrate reduction is explained in terms of acid-base catalysis, involving species diffusing as La(III)-nitrate complexes (ion pairs) close to the silver electrode.