An investigation has been made of the effect of benzene on the isomerization of n-pentane on palladium catalysts based on Y, mordenite and TsVM zeolites. The palladium content of the catalysts was varied from 0-001 to 0-5 wt.%. It was shown that, in the presence of benzene, there is a reduction in the isopentane yield, and isomerization is less selective. The activity of catalysts in isomerization and cracking increases with their palladium content. The hydrogenation of benzene begins with palladium contents of 0.05-0.1 wt.%. It was established that hydrocarbon cracking and isomerization occurs on acid centres of the catalyst. Here, in the case of catalysts based on HTsVK the state of the acid centres is such that the intermediate carbonium ions on them act like radicals. This is indicated by the magnitude of the isobutane/n-butane ratio in the cracking products. The results obtained are explained on the basis of the bifunctional mechanism of action of the catalyst and by movement of the isomerization of n-pentane in the presence of benzene to acid centres of lower strength.