Desorption and oxidation of presorbed ammonia and pyridine on H-mordenite were carried out in a differential scanning calorimetry (DSC) cell in nitrogen and oxygen atmospheres. Adsorption of ammonia on the strong acid sites of the zeolite were found to be less strong than the adsorption of pyridine on these sites. In a current of nitrogen, no decomposition of the investigated bases took place up to 600 degrees C. Oxidation of pyridine on H-mordenite occurred at higher temperatures than the oxidation of ammonia. DSC thermograms could be completed by decreasing the heating rate.