The specific activity of vickel catalysts promoted with alumina/chromia-mixtures for the isotopic exchange of deuterium between hydrogen and water vapour decreases to a great extent due to water condensation on its surface. To overcome this difficulty, it is essential to search for a catalyst of high activity in both liquid and vapour phases. The isotopic exchange reaction was used as a test reaction in the vapour phase, while the thermal decomposition of hydrogen peroxide was chosen as a simple test reaction in the liquid phase. Activity measurements in both liquid and vapour phases indicate that the catalyst composed of 85 mol% Ni/10 mol% Al2O3/5 mol% Cr2O3exihibits maximum activity on both phases.