Pervaporative separation of benzene from its mixture with cyclohexane over the entire concentration range 0-100% benzene was studied using three copolymer membranes of acrylonitrile. The other monomers in the copolymers were selected on the basis of their solubility parameter values relative to those of benzene and cyclohexane. These were styrene, methyl methacrylate, and vinyl acetate. For each copolymer of acrylonitrile three different membranes with different copolymer compositions were prepared. Copolymers of acrylonitrile with methyl methacrylate and vinyl acetate showed good selectivity and moderate flux (0.075 kg/(m(2) h) and 60-70 with a membrane of 10 mu m thickness for a feed mixture containing 5% benzene). A copolymer of acrylonitrile with styrene showed comparatively higher flux but lower selectivity. The selectivities obtained with these copolymers are better than those reported in the literature.