The kinetics of the hydrogen electrode reactions on Pt in the NaHSO4 + KHSO4 melt at ca. 185°C is studied. Under potentiodynamic conditions both the anodic and cathodic processes can be interpreted with the hydrogen electrode reaction mechanism already known. At potentials more negative than 0.1 V (vs. Ag/Ag+ (0.06 M)) the mechanism of the cathodic reaction changes because of a sulphide species formed on the electrode which is produced by a reduction of the melt components.