The vapour phase reduction of various aliphatic ketones to the corresponding carbinols by propan-2-ol in the presence of MgO as a catalyst has been studied. A strong decrease of the reactivity (from 86 to 0%) in the reduction of pentan-3-one and its polymethyl derivatives with an increase of the bulkiness of both alkyl groups in the ketone has been observed. For ketones with the general formula CH3-(CH2)(n)-CO-(CH2)(8-n)-CH3, where n = 0, 1, 2, 3 and 4, a shift of the carbonyl group to the middle of a molecule causes only a small decrease of the reactivity. It has been stated that the observed changes in the reactivity of ketones are mainly caused by a steric hindrance around their carbonyl groups.