Ammonia is formed during potentiostatic reduction of sodium nitrite solutions on the nafion-complex-coated electrode. When (NH4)(2)[MoO2(O2CC(S)(C6H5)(2))(2)] is present in NaNO2 solutions a polarographic wave is associated to electroacatalytic reduction of nitrite ion. The wave height varies linearly on the concentration of nitrite ion, allowing a procedure for analysing this ion. This electrochemical behaviour distinguishes the nitrite from the nitrate ions. The Mo(VI), Mo(V), and Mo(IV) are involved in catalytic redox processes determining formation of NH4+ from nitrite ions.