The effect of hydrogen sulphate ion on the hydrogen and methanol oxidation reactions was examined on t(111), Pt(100) and Pt(110) electrodes by a voltammetric method. The comparison of the voltammograms obtained with and without the dissolved H-2 and CH3OH showed a strong specific adsorption of hydrogen sulphate ion on Pt(111) and then on Pt(100) but no effect on Pt(110) in the time interval of a potential scan of 50 mV s-1. The methanol oxidation reaction proceeded ca. 80 times faster on Pt(110) than on Pt(111) in 0.5 M H2SO4 and suffered self-poisoning most strongly on Pt(110) and least on Pt(111). Common to both the hydrogen ionization and methanol oxidation reactions, a strong retardation appeared in a potential region just before the commencement of the oxygen wave on the respective planes in H2SO4 and HClO4 solutions. A compact reorientation of the water molecule in this potential region is discussed as a candidate for the retardation.