A crossflow membrane filtration process was developed to separate soluble intracellular protein from the debris and inclusion bodies present in a recombinant Escherichia coli cell lysate. Membranes with different chemistries, pore sizes and configurations were screened for high-permeate flux, protein transmission and recovery of water flux after cleaning. Cleaning efficiency was one of the criteria used to select membranes for further testing. To determine the desired transmembrane pressure (TMP), a 0.1 mu m polyethersulfone membrane was selected for additional testing at different TMPs with longer process times. Classic limiting flux behavior was observed with TMPs greater than 55 kPa giving no additional improvement in permeate flux. Finally, 84% of the soluble material was removed after 3 volumes of a constant volume diafiltration. (C)2000 Elsevier Science B.V. All rights reserved.