A major limiting step in the use of pressure-driven membrane processes is the membrane fouling, and this is the single most important reason for the relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. In the present study the variations of the active membrane area with time is evaluated, during the membrane fouling and cleaning with an electric field applications. These operations are characterized by means of some technical parameters described by a mathematical model that interprets the exponential variation of permeate fluxes and permit evaluate the extent of the membrane fouling and cleaning with electric fields. An efficient factor for the cleaning process is defined as a function of active membrane area. The expressions obtained let to evaluate the ultrafiltration of BSA solution and may be applied to other UF systems with different characteristic of the one considered in this study. (c) 2006 Elsevier B.V. All rights reserved.