Membrane fouling is one of the critical factors that determine a membrane's lifetime and the effectiveness of filtration processes. Thus, the use and optimization of chemical cleaning is crucial. In this study, a confocal scanning laser microscope (CSLM) along with macroscopic results (permeate flux evolution) was used to evaluate the effectiveness of water rinsing and chemical cleaning protocols on polycarbonate membranes fouled with model solutions containing BSA and dextrans. Water rinsing for 30 min as well as chemical cleaning cycles of 5,15 and 30 min with two different concentrations of an enzymatic cleaning agent (P3 Ultrasil 53) were tested. CSLM was used to calculate the fraction of pore surface where protein and/or dextran were detected (P-s) and to obtain qualitative information from 3D image reconstructions, all of which provided information about membrane fouling by the protein and the dextrans. From the analysis of the P-s profiles, water flux recovery and CSLM images, it is clear that water rinsing does not improve membrane permeability if protein is involved in membrane fouling. It is shown that during water rinsing some of the proteins are driven deeper inside the membrane, causing further blockage and reducing water flux. As for chemical cleaning protocols, the cleaning operating conditions (concentration of the cleaning agent and cleaning time) which resulted in the highest water permeate flux recovery were determined. From P, Profiles and CSLM images, it was seen that most of the protein and the dextran were removed from the membrane during chemical cleaning. (c) 2008 Elsevier B.V. All rights reserved.