The work describes the functionalization of microporous poly(ether imide) membranes with ultrafiltration separation profile by degradative functionalization using a two-step treatment process, which leads to strongly aminated membranes with microfiltration properties. Membranes with different morphology and ultrafiltration separation profile were prepared. In the first step, the pore system was opened by treatment with diethylenetriamine (DETA) which was followed by a treatment with high molecular poly(ethylene imine) to increase the amount of amine groups. Results verify that macrovoidal structures are more beneficial than sponge-like structures because of their strongly opened pores while only a small reduction in membrane thickness occurred. The separation properties of the virgin membrane have only a marginal influence on the pore opening process because of the leveling off the separation properties after a short treatment time. The number of covalently bound amine functions could be strongly increased by a second step functionalization process using a high-molar volume polyamine as a modifier which indicates the presence of residual imide groups of the basic polymer after the primary DETA treatment. Moreover the prepared membranes are suited for steam sterilization. These characteristics suggest a beneficial application in adsorptive separation processes. (c) 2007 Elsevier B.V. All rights reserved.