The elementary steps of alkylation of ammonia with ethanol and the role:of the strength and location of the acid sites of the mordenite catalysts were investigated by means of in situ i.r. spectroscopy, temperature-programmed desorption and kinetic measurements. Ethanol and ammonia have access to all Bronsted acid sites of the mordenites investigated. From the products only monoethylamine reached all acid sites, while di- and triethylamine sorbed only on 60% and 45% of the sites, respectively. The Bronsted acid sites of HNa-mordenites are exclusively located in the main channel up to an hydrogen exchange degree of 60%. Only at higher exchange degrees are the sites in the side pockets also exchanged. These latter acid sites apparently contribute significantly to the overall rate of amination. Mordenite with a high concentration of Na+ ions (low H+ exchange degree) stabilize ammonium less than those with a low Na+ concentration. This leads to more ethene produced dukng: the amination reaction. While some diethyl ether is:formed during amination, the alcohol and not the ether is the primary alkylating agent.