Ion exchange and water content measurements were performed with an anion exchange membrane, ADS XL 10 (Solvay), equilibrated in aqueous solutions containing mineral electrolyte as NaCl, and/or organic electrolyte as sodium benzene carboxylate (Phi CO2Na) and sodium 4-hydroxy-1-naphthalenesulfonate (Phi Phi OHSO3Na). By using radiotracers, it was possible to determine the amount of the total mineral and organic ionic species present inside the membrane. The fixation of big organic ions balancing the exchanging sites of the membrane can modify the membrane structure, creating micropores able to sorb more electrolytes. It was established that the sorption of hydrophobic organic ions corresponds to a ’micelle mechanism’, The penetration of hydrophobic ions into the membrane induces a change in the molar volume of the wet membrane in relation to the variation of the water content.