The aim of this work was to study the impact of acidification and basification pre-treatment on the integrity and the susceptibility of anion- (AEM) and cation- (CEM) exchange membranes to fouling by peptides. The acidification and basification of ion-exchange membrane interfaces appear during electrodialysis when the limiting current density is reached. At this point, the mass transport of ions is no more sufficient for current transport and this leads to the water molecule dissociation. Thickness, conductivity and nitrogen content of ion-exchange membranes were evaluated after a pre-treatment of the membranes by soaking them in distilled water (DW), HCl (1 N) or NaOH (1 N) for 24h and once again after soaking them in a soy protein hydrolysate solution (SPHS) for another 24h. Results indicated that whatever the pre-treatment was, peptides tend to react with each kind of membrane, and that, with no application of current. CEM soaked in HCl showed the highest increase in peptides content. During this treatment, H(+) reacts with the external and internal fixed groups of the CEM which are negatively charged. Then, the presence of H(+) at the membrane interface causes peptides, negatively charged at the SPHS pH (around 6.2), to react with the membrane and to form a fouling. Washing solutions of salt (NaCl 2% and 5%) removed most peptides after soaking for 24 h. This result indicates that electrostatic interactions are the main links formed during membrane fouling by peptides without application of current. (C) 2010 Elsevier B.V. All rights reserved.