A simple and inexpensive treatment for surface functionalization and grafting carried out under mild aqueous conditions and suitable for prefabricated medical devices, has been developed. The two stages are performed separately; the first is hydroxylation by a peroxy compound, particularly a peroxydisulfate or peroxymonosulfate, in aqueous solution with strong nitrogen purging; and the second is grafting of a vinyl monomer by the conventional ceric ion technique. Types of polymer studied include polypropylene, polystyrene, polyacrylonitrile, polyurethanes, aliphatic polyesters, nylons, aromatic polyesters and polycarbonates. Surface properties of the substrate polymers may be greatly modified by this treatment. To illustrate possible applications for covalent coupling of bioactive molecules to polymers we have attached the blood-anticoagulants heparin and hirudin to the polyester Ecdel and to polystyrene, respectively. The products were highly bioactive.