Amongst the alternative fuels obtained from renewable resources alcohol from fermentation may become one of the most important. The combination of fermentation with pervaporation in a membrane bioreactor offers the advantage of continuous processing. In this membrane bioreactor alcohol-selective membranes are needed. The performance of the membranes available at present is poor. Much research is being carried out on silicone rubber but the selectivity of this material for alcohol is too low. Addition to the membrane of a sorptive filler with a high selectivity towards alcohol appears to improve both selectivity and flux. Silicalite, a novel type of hydrophobic zeolite, has been used for that purpose. Results presented in this paper indicate that transport through the zeolite pores contributes to a major extent to the total transport through the membrane.