The H-D exchange between alkanes and zeolites normally proceeds with the formation of adsorbed carbenium ions and olefins as intermediates. Cycloalkanes were used to study the regioselectivity and stereochemistry of the elimination/protonation reactions on zeolites to establish the role of the framework in proton transfer reactions. A preferential exchange in the secondary equatorial position adjacent to the tertiary center, relative to the axial one was observed. This result is in agreement with recent theoretical calculations of elimination/protonation reactions occurring on the zeolite surface, which point out that an eclipsed conformation between the eliminating proton and the cationic center is necessary for the reaction to take place. Therefore, in cycloalkanes, the equatorial hydrogens can be better accommodated in the eclipsed orientation, This result is in opposition to what is observed for elimination/protonation reactions of cycloalkanes in solution, where the axial protons are easier eliminated, With t-butyl-cyclohexane an almost exclusive exchange at the methyl position was observed, This result cannot be explained by the present accepted mechanism involving olefins and carbenium ions.