Heterogeneous surface modifications of polyacrylonitrile (PAN) ultrafiltration (UF) membranes with either simultaneous or sequential UV irradn.-initiated graft polymns. of monomers from water solns. were studied. Previous coating with a photo-initiator (benzophenone, BP) and satn. of the monomer solns. with BP mainly promoted simultaneous graft polymn. onto the membrane surface. Photo-induced formation and thermal decompn. 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 concn. was described. The polymn. conditions could be used as means to adjust the total degree of graft polymn. (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/cm2) the modified layer on the outer surface was thin (400 mg/cm2) reduced contact angles, very little protein adsorption and almost no fouling due to bovine serum albumin (BSA) adsorption were obsd. Results of UF expts. with g-globulins, BSA and cytochrome C, applied as single and mixed protein solns., suggested that with PAN-g-MePEG200MA, in contrast to the unmodified PAN UF membranes, protein/protein UF sepns. may become feasible because protein/polymer surface interactions are diminished.