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The catalytic activity of the substoichiometric tungsten trioxide electrodes for the oxidation of hydrogen has been investigated, using simultaneous EPR spectroscopy and linear-sweep voltammetry measurements. The parameters of the EPR spectral line observed for all oxides except stoichiometric WO₃ were determined in relation to the electronic structure of the paramagnetic centers associated with the oxygen anion vacancies. Hydrogen adsorption was followed by means of changes both in the EPR line parameters and in the electrode potential. The intensity-versus-potential curves for suboxide electrodes under hydrogen were analyzed in terms of the occurrence of two processes. It was shown that one process is associated with the hydrogen oxidation and that the other is connected with oxidation of the WO_3?x surface. The mechanisms of both reactions were interpreted as involving the formation and oxidation of an hydrogen tungsten bronze.