The vibrational perturbations induced in the IR spectra of methane and of dihydrogen by the non-dissociative adsorption on the (01 (1) over bar 2) and (11 (2) over bar 0) faces of alpha-chromia are illustrated and compared. It is concluded that both molecules are adsorbed on Cr3+ sites and that the involved forces are mainly of the electrostatic type. The resulting situation is compared with that found on the more basic MgO. The problems associated with the C-H and H-H bond activations on transition metal oxides are also discussed.