The trivalent chromium transport through Nafion(R) 117 cation-exchange membrane was studied by electrochemical impedance spectroscopy (EIS). Results showed the presence of an interfacial charge transfer component characterising the exchange of Cr3+ ions between the solution and the membrane and a bulk diffusion component relative to the transport of the chromium ions through the membrane. This bulk diffusion component was explained as a coupling between the diffusion of Cr3+ ions and a chemical reaction due to the formation of a transient coordination complex of Cr3+ ions and the sulfonate groups. A dependence on the pH of the solution was also observed, suggesting a mixed diffusion of Cr3+ and H+ inside the membrane phase. (C) 2003 Elsevier Science B.V. All rights reserved.