The catalytic behavior of several supported nickel catalysts in the hydrogenation of acetonitrile was studied. It was established that the selectivity of this process is greatly influenced by the nature of the support used. Catalysts consisting of nickel supported on acidic supports catalyzed the formation of condensation products, diethyl- and triethylamine. Nickel supported on basic supports was highly selective with respect to the formation of the primary amine, ethylamine. It was shown that modification of the intrinsic acidity of alumina-based supports by the application of alkaline additives has a large impact on the selectivity of the resulting catalyst. Based on the results obtained from measurements on a basic catalyst diluted with either an acidic or a basic support, a dual-function mechanism is suggested. The mechanism implies that the hydrogenation function of the catalyst is located on the metal, while the acid function, responsible for the condensation reactions, is located on the support. A mechanism, accounting for the occurrence of the acid-catalyzed condensation reactions, is proposed.