Reactions of tetralin with tritiated gaseous hydrogen were carried out at 5.00 MPa and at 200-400 degreesC on several noble metal catalysts prepared: Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3. Hydrogenation and dehydrogenation activities of the catalysts were compared. By tracing changes in the radioactivities of H-3 in the products before and after reaction, amounts of the hydrogen exchange between tetralin and tritiated hydrogen were measured to determine the behavior of hydrogen in the reaction. Further, effects of sulfur present in the feedstocks on the catalytic performance were investigated and resultant differences in the sulfur tolerance among the catalysts were clarified.