The influence of pressure and temperature on the catalytic behaviour of H-beta zeolites in the conversion of sec-butylbenzene, an hydrocarbon present in reformed gasoline, has been investigated. The reaction pathway involves many parallel and/or successive steps, the main reactions being dealkylation, isomerization and disproportionation. The activity and stability of the catalyst increase with increasing pressure. Products distribution is also affected by pressure. An increase in temperature leads to an increase in both conversion and selectivity to dealkylation. The disproportionation and isomerization products are favoured at low temperatures. A general scheme of the process is proposed on the basis of the structural and acidic features of the catalyst. (C) 2002 Elsevier Science B.V. All rights reserved.