The effect of 5, 10 and 15 g/L glucose or 5 and 10 g/L xylose on the efficiency of ethanol pervaporation through a polydimethyl-siloxane membrane was studied using a 2% w/w aqueous ethanol solution. Membrane total flux and ethanol selectivity were measured at solution feed temperatures of 40, 50 and 60 degrees C and permeate-side pressures of 1, 10, 20 and 40 mm Hg. Glucose at 15 g/L decreased total flux by 8% at a temperature of 60 degrees C and a pressure of 40 min Hg while ethanol selectivity was decreased by 15.3%. Xylose had practically no effect on total flux and a slight effect on selectivity which interacted with temperature.