Heterogeneous surface modifications of PAN UF membranes with either simultaneous or sequential UV irradiation-initiated graft polymerizations of monomers from water solutions were studied. Previous coating with a photo-initiator (benzophenone, BP) and saturation of the monomer solutions with BP mainly promoted simultaneous graft polymerization onto the membrane surface. Photo-induced formation and thermal decomposition of peroxides were assayed with the DPPH assay and then used for sequential grafting, For both approaches, and with acrylic acid, 2-hydroxyethyl methacrylate and various poly(ethylene glycol) methacrylates (PEG-MA’s and MePEG-MA’s) the impact of photo-initiation as well as monomer type and concentration was described, The polymerization conditions could be used as means to adjust the total degree of graft polymerization (DG) and the graft polymer chain length, Modified membranes were characterized with FTIR-ATR spectroscopy and contact angle measurements; the main conclusion was that even at high DG (1-2 mg/cm(2)) the modified layer on the outer surface was thin (< 1 mu m) acid the modification extended into the active layer pores of the membranes, Membrane permeabilities diminished systematically with increasing graft polymer mass. For UF membranes with sufficient degree of modification (DG > 400 mu g/cm(2)) reduced contact angles, very little protein adsorption and almost no fouling due to BSA adsorption were observed. Results of UF experiments with gamma-globulins, BSA and cytochrome C, applied as single and mixed protein solutions, suggested that with PAN-g-MePEG200MA, in contrast to the unmodified PAN UF membranes, protein/protein UF separations may become feasible because protein/polymer surface interactions are diminished.