The hydrodenitrogenation (HDN) reactivities of indole (IND) and several methyl-substituted indoles (MIN) were determined over a NiMo/Al2O3 catalyst and a CoMo/Al2O3 catalyst using a fixed-bed reactor at 340 degrees C and 31 atm hydrogen pressure. Appreciable differences in reactivity were obtained, depending on the location of the methyl group. Compared to IND, overall conversions and HDN conversions were generally higher when methyl groups were on the aromatic ring, and substantially lower for methyl groups on the N ring. Two paths for initial conversion of IND (MIN) were deduced, viz., a CNH path (C-N bond cleavage) and a HYD (aromatic hydrogenation) path. The NiMo catalyst favored the HYD path over the CNH path, while the opposite occurred for the CoMo catalyst. Reasonable trends were obtained between initial CNH rates and the electrostatic potential on the N atom of the MINs, and between initial HYD rates and the ionization potential. (C) 2000 Academic Press.