The electrochemical reduction of electrodeposited MnO2 on Pt electrodes has been investigated in sulphuric acid solutions by means of linear sweep and cyclic voltammetry. The influence of pH, temperature, Mn2+ concentration and conditioning at fixed cathodic potentials has been considered. The cathodic voltammograms are characterized by an intense single peak. The formation of a scarcely conducting thin surface layer on bulk manganese dioxide accompanies the reduction peak. This layer, whose thickness depends on pH and Mn2+ concentration, limits the reduction rate of manganese dioxide so that, after the current peak, the reduction process continues under limiting current conditions. The overall results allowed a useful definition of the electrochemical activity of MnO2.