In order to optimize the reaction conditions for the process of silver deposition from thiosulphate solutions, the knowledge of the mechanism of the reduction reaction is required. In the present paper, the role played by NaNO3 (added as supporting electrolyte) and Na2S2O3 (complexing agent for Ag+) on the reduction process is studied by means of ac impedance and surface-enhanced Raman spectroscopy (SERS). In a solution made up of 0.1 M NaNO3, 0.025 M Na2S2O3 and 1 x 10(-3) M AgNO3 (pH = 12), with an equilibrium potential E(0) of -215 mV/sce, the reduction follows a CE mechanism, but divergences are found at overvoltages smaller than 30 mV. SERS measurements on a pretreated silver electrode showed that at potentials between E(0) and about -250 mV/sce, the adsorption of S2O32- is stronger than at more cathodic potentials. The effect of the enhanced S2O32- adsorption on the electrochemical behaviour is hidden in solutions containing more NO3- by an overall acceleration of the reduction rate.