To reduce the problems with fouling and concentration polarization during crossflow ultrafiltration of industrial enzyme solutions an electric field is applied across the membrane. The filtration performance during electro-ultrafiltration (EUF) has been tested with several enzymes. Results show that EUF is an effective method to filter high concentrated solutions at low crossfiow. The flux improved 3-7 times for enzymes with a significant surface charge at an electric field strength of 1600V/m compared to conventional UF. The greatest improvement is observed at high concentration. Not all enzymes can be filtered with EUF, mainly due to a low surface charge and impurities in the feed solution. Using a pulsed electric field did not improve the flux compared to a constant field. Gel electrophoresis experiments of the enzymes appear to be a useful method for estimating the influence of the electric field. (c) 2007 Elsevier B.V. All rights reserved.