Organic/water mixtures are separated at ambient temperature and pressure by pervaporation through a silicalite zeolite membrane supported on the inner surface of a porous stainless-steel cylindrical tube. Methanol, ethanol and acetone were preferentially separated from aqueous solutions. For methanol/water separations, a relatively constant separation factor between 11 and 14 was obtained over a wide range of methanol feed concentrations. Total mass fluxes of 1 to 2.7 kg/(m(2) h) were obtained. Water and methanol permeances were independent of methanol feed concentration, except at low concentrations. Pervaporation has a higher separation factor than expected for vapor-liquid equilibrium separation. The highest separation factor obtained for acetone/water was 255 at an acetone feed concentration of 0.8 wt% with an acetone flux of 0.20 kg/(m(2) h). The highest acetone flux of 0.95 kg/(m(2) h) was obtained at an acetone concentration of 43 wt%, when the separation factor was 37. Separation factors decreased. with increasing acetone concentration. The production indices for the silicalite membrane were much higher then other membranes at similar feed concentrations. The silicalite membrane was unable to selectively remove acetic acid from aqueous solutions at low acid concentrations.