The hydrodesulfurization of cyclohexanethiol and 2-methylcyclohexanethiol was studied over a sulfided NiMo/gamma -Al2O3 catalyst. About two-thirds of the thiols reacted by elimination to (methyl)cyclohexene and one-third by hydrogenolysis of the C-S bond to (methyl)cyclohexane. These values are slightly lower than those for the selectivity to methylcyclohexene and slightly higher than those for the selectivity to methylcyclohexane in the hydrodenitrogenation of 2-methylcyclohexylamine. In aliphatic molecules that contain H atoms in the beta position relative to the nitrogen atom, hydrodenitrogenation occurs predominantly (70-80%) by elimination of ammonia. Part of the remaining (20-30%) hydrodenitrogenation takes place by nucleophilic substitution of the amine by H2S, followed by elimination of H2S from the resulting thiol and, to a lesser extent, by C-S bond hydrogenolysis; the rest of the remaining hydrodenitrogenation takes place by direct hydrogenolysis of the C-N bond.