A series of novel charged ultrafiltration membranes that differed in spacer arm length and charge group functionality was developed using epichlorohydrin (EPI) activation of a commercially available regenerated cellulose membrane. Hydraulic permeability and protein retention data were obtained over a range of ionic strength using cytochrome, c as a model protein. Membrane properties were also examined using dextran sieving, streaming potential, and counter-electro-osmosis measurements. The results clearly demonstrate that considerable improvements in membrane performance can be achieved by proper design of the membrane charge functionality, and in particular the spacer arm length, providing new opportunities for optimization of ultrafiltration membranes for bioprocessing applications. (C) 2008 Elsevier B.V. All rights reserved.