The preparation of polymer surfaces for the immobilisation of biologically active molecules comprises an activation to form reactive groups and a specific functionalisation starting from these groups. A low-pressure oxygen plasma is an excellent tool for the activation of the inner surface of a millimetre sized porous polyolefin material. For this functionalisation, a concise set of reactions and substances can be used to prepare well-defined surfaces with a coupling group (-COOH or -NH2, 16 nmol/g) on a variable spacer chain. Diamine functionalised polypropylene oxide is suited very well as spacer for the immobilisation of the fluorescing protein DsRed, which was chosen as a model protein. The same surface chemistry can also be used to couple a copolymer containing ammonium units and amine units. The resulting surface shows unique anti-microbial properties. (C) 2004 Elsevier B.V. All rights reserved.