n-Pentane and o-xylene isomerizations have been studied at 285 and 150-degrees-C, respectively, on seven dealuminated H-mordenites containing different amounts of framework and nonframework aluminum which were prepared by steaming or calcining NH4-mordenite. The number of Bronsted and Lewis sites were known beforehand from Si-29 high-resolution magnetic resonance and infrared study of low-temperature CO adsorption. In addition, the availability of the acid sites to the reactants was estimated from the ratios of the liquid monolayer volume of the reactant (n-pentane or o-xylene) to that of N2, the availability of the active sites to N2 and CO being the same. It was observed that the initial rates of isomerization divided by the number of available Bronsted sites are proportional to the number of available Lewis sites. This observation suggests a synergistic enhancement of the acidity by the interaction between Bronsted and Lewis acid centers. Other aspects related with the products distribution are also discussed.