Alcoholic hydroxyl groups were introduced into a polyethylene microfiltration (MF) membrane by radiation-induced graft polymerization of 2-hydroxyethyl methacrylate (HEMA), vinyl acetate (VAc), and glycidyl methacrylate (GMA). Subsequently, the VAc- and GMA-grafted membranes were quantitatively hydrolyzed into monool (single hydroxyl) and diol groups, respectively. The pure water flux of the modified membrane and the saturation Capacity of bovine gamma-globulin onto the membrane were determined as a function of alcoholic hydroxyl group density. The threshold value for hydrophilization ranged between 5 and 7 mol of alcoholic hydroxyl group per kilogram of original MF membrane. Masking of the polyethylene surface with grafted polymer branches containing the diol groups was effective because approximately 70 % of the pure water flux of the original MF membrane was maintained. Irrespective of the pore diameter of the original MF membrane, saturation capacities on the modified membrane correlated well with the diol group density. Saturation capacities of bovine gamma-globulin and bovine serum albumin were reduced to 1 mg/m(2) of the membrane. In addition, the binding interaction changed from irreversible to reversible.