The broad application of hollow fiber micro-bioreactors in various areas of biotechnology is still restricted due to a limited functionality of the membranes. With this paper a straight forward procedure for membrane functionalization is presented. Different commercially available polyethersulfone (PES) and polysulfone (PS) hollow fiber membranes were chemically modified by reacting terminal hydroxyl groups with ethylene glycol diglycidyl ether (EGDGE) to produce terminal epoxy groups. For increasing loading capacity hydroxyethyl cellulose polymers (HEC) were bound to the epoxy groups. Second epoxidation produced final polymers containing reactive epoxy groups on the hollow fiber surface. From this modified PES and PS, respectively, a wide variety of N-containing reagents (e.g. iminodiacetic acid (IDA)) can be bound to the epoxy groups. The different reactions were proved by acid orange II assay and phenol sulfuric assay. To assure intact hollow fiber surface after membrane modification scanning electron microscopic analyses were performed. The chelating IDA-membranes were complexed with different divalent metal ions (CU2+ Ni2+, Co2+, Zn2+). Immobilized metal ion affinity PES hollow fiber membranes were used for purification of a recombinant protein (GFP-His) from Escherichia coli, which carried a polyhistidine sequence (His(6)-tag). Determination of bound and unbound GFP-His(6) was performed by fluorescence spectroscopy, Bradford assay and SDS-PAGE. (c) 2007 Elsevier B.V. All rights reserved.