A method is provided for conversion of heavy alkylaromatic compounds, particularly those in the C8-C12 range, into more valuable aromatics of benzene, toluene and xylene utilizing a toluene disproportionation unit containing a nickel, palladium or platinum-modified mordenite catalyst. The method allows large amounts of these heavy alkylaromatic compounds to be processed without adversely affecting catalyst activity or catalyst life. This is accomplished by introducing the heavy alkylaromatic compounds into the reactor at constant reaction severity conditions and maintaining those conditions during conversion.