The promoted electro-oxidation of aqueous sulphur dioxide at platinum electrodes has been studied in acidic medium with the aid of cyclic voltammetry and in-situ FT-IR spectroscopy. Promotion of SO2 oxidation is achieved when adsorbed SO2 is reduced previously to adsorbed sulphur. On a platinum surface covered by sulphur in this way, an enhancement of SO2 oxidation is attained. Spectroscopic evidence demonstrates that, like oxidation of SO2 in the oxygen adsorption region, soluble S(VI) is the ultimate reaction product of the catalysed SO2 oxidation. The electroreduction of SO2 has been dealt with by using the same techniques. Besides a surface process converting adsorbed SO2 into adsorbed sulphur, bulk SO2 reduces irreversibly giving rise to a diffusion-limited voltammetric peak. The absence of significant IR bands in the potential region at which reduction of built SO2 takes place, allows discarding the generation of S-H containing species. A sulphur + polysulphide mixture is suggested as the ultimate product, yet whether this mixture is formed directly in the electron-transfer step or stems from chemical decomposition of sulphur-oxygen short lifetime intermediates is not clear. Reduction of SO2 leads to a progressive accumulation of sulphur on the platinum surface. An excess of adsorbed sulphur negatively affects the kinetic stages of both oxidation and reduction of bulk SO2.