Radiation-induced graft copolymerization of styrene/maleic anhydride (Sty/MAn) binary monomers into high-density polyethylene (HDPE) has been studied. The optimum conditions under which a high grafted yield is obtained and the grafting process proceeds homogeneously have been determined. A suitable solvent for the grafting process is acetone for a (Sty/MAn) composition of (70/30 mol%). The permeability of low molecular weight metabolites (urea, creatinine, uric acid, glucose and phosphate salts) through the untreated and treated grafted HDPE membranes has been studied. The hydrophilicity of the membrane, the degree of grafting and the molecular weight and chemical structure of the metabolites have a great in¯uence on the transport properties of the membrane. For all solutes investigated, the permeability increases with the degree of grafting. The basic metabolites show higher permeation rates through the modi®ed membrane compared with that for the acidic metabolite, especially phosphate salts. The permeabilities of vitamin B 12 , bovine albumin and KCl through the treated grafted membranes have been measured and those of the high molecular weight compounds are low.