A simple membrane process for the protein fractionation has been developed using suffortated poly(ether sulfone) ultrafilter membrane under coupled driving forces (pressure and potential difference). Different extent of sulfonation of poly(ether sulfone) was carried out under controlled conditions and negatively charged membranes with different charge density were prepared under optimum conditions. Ionic functional groups incorporated into polymer have decided effect on physical properties of the ultrafilter membrane. Apparent pore radius of these membranes was estimated by water permeation studies, while electro-osmotic permeation data was used for the determination of zeta potential under given environment. A systematic study on the effects of pH or nature of the charge on the bovine serum albumin on its adsorption characteristic using these charged membranes was carried out. Transmission of proteins (bovine serum albumin (pi = 4.8) and lysozyme (pl = 10.7)) across these membranes were studied under simultaneous action of pressure and electrical gradient at pH points: 2.0, 4.8, 10.7, and 13.0 (pH > pl or pH < pl). Polarity of electrical potential was set in such a way that both type of migrations (pressure or electrical driven) occurred in the same direction. It was observed that transmission of protein can be governed by varying nature of the charge on it (pH), nature and extent of the charge on the membrane matrix, polarity of the applied potential gradient with an ultrafilter membrane of given pore dimensions. In this novel processes, charge on the protein, nature and extent of the charge on the membrane interfaces, polarity of the potential gradient all are governing the transport of given protein across the membrane, which resulted high selectivity and membrane throughput under coupled driving forces. (c) 2007 Elsevier B.V. All rights reserved.