The performance of supported nickel catalysts in the disproportionation of n-propylamine was studied. Although hydrogen is not needed as a reactant, it is observed that in the absence of hydrogen the activity of the catalysts is low. Furthermore, deactivation of the catalysts by carbon deposition and nitride formation occurred when hydrogen was not present. In the presence of hydrogen, deactivation by carbide formation was suppressed. At high hydrogen concentrations deactivation of the catalysts was completely inhibited. During the reaction in the presence of hydrogen, all catalysts formed dipropylamine with a high selectivity (more than 98 mol-%). Without hydrogen, however, unsaturated molecules were the main products (imines, Schiff bases). This observation was explained by a bifunctional mechanism; propylamine is first dehydrogenated on the metal to the imine, which is converted subsequently to the Schiff base on the acid sites of the support. In the absence of hydrogen these compounds are not hydrogenated and leave the catalyst bed. It was demonstrated that the activity of a particular catalyst in the disproportionation reaction is related to its acidity. The existence of a linear relationship between the conversion of propylamine and the selectivity toward ethylamine in the hydrogenation of acetonitrile proved that the acidity of a catalyst is responsible for the occurrence of the condensation reactions leading to secondary and tertiary amines. The disproportionation of n-propylamine is a new and highly reliable catalytic test reaction to measure the acidity of supported nickel catalysts.