The permeation rates of ethanol and methanol vapours through alumina membranes with pore diameter of 5 and 10 nm were measured in the temperature range 150-200 degrees C. The permeability of ethanol and methanol vapours is less than that predicted from a model which combines bulk viscous and Knudsen flow. A new model based on the assumption that the contribution of the adsorbed phase of ethanol and methanol on the membrane pore wall is small compared to that in the gas phase is proposed. Experiments with nitrogen-ethanol and nitrogen-methanol mixtures were conducted to verify this assumption. The proposed model describes the behaviour of the mixtures well, though low temperature data with the 5 nm membrane do not agree so well with the model.