Ultrafiltration (UF) membranes from polysulfone (PSf) were functionalized by heterogeneous photo-initiated graft copolymn. of acrylic acid (AA). With radiation susceptible PSf, only proper selection of the UV energy (l > 350 nm; for selective excitation of the photoinitiator) yielded membranes with preserved UF barrier layer. Possibilities for adjusting structure and morphol. of the graft polymer (g-PAA) layer by variation of functionalization parameters such as AA concn. and UV irradn. time were investigated. Very long grafted chains (MW > 105 g mol-1) at varied grafting d. (GD = 0.01... 1.2 nmol cm-2, relative to the outer surface area) were obtained. Partial penetration of the UF barrier layer by g-PAA was verified. Covalent immobilization of bovine serum albumin (BSA), g-globulin (g-Gl) and alk. phosphatase (APh) was achieved by coupling with a water sol. carbodiimide. Bound BSA and g-Gl amts. were up to G = 10 mg cm-2, for membranes accessible only from the outer surface thus not using the entire pore vol. Locally addressed covalent protein immobilization after photo-patterning the PSf surface could be visualized with a fluorescent FITC-BSa conjugate. A strong salt effect onto immobilized APh activity (increase with NaCl concn.) was obsd., indicating internal transport/accessibility limitations in the g-PAA layer. Correlations between PAA structure (MW, GD) and accessibility (from BSA or g-Gl binding and APh activity) could be established. The 'tentacle' g-PAA functionalized PSf UF membranes having preserved UF barrier and, e.g., with surface-bound receptors will find application in cell cultures under diffusion or perfusion conditions.