The paper presents the results of experimental and theoretical investigations of an electrodeionization process for the removal of metal cations from dilute solutions. The ability of this technique to treat 100 ppm copper solutions using cationic membranes and ion-exchange resins between the membranes was studied. Fair abatement yields were obtained in the 100 mm high resin bed in long-term runs, and solutions of an appreciable copper ion concentration could be produced in the cathode chamber. The process capacity was limited by significant deposition of copper at the cathode, non-even distribution of current density, and side-diffusion to the anode chamber. Additional tests were then carried out using a 15 mm resin bed. The more even current distributions allowed the effect of the resin stiffness and the current density on the removal yield to be thoroughly observed. Steady-state operation of the resin bed was modelled using generalized expressions of the various transport rates. Results of the model clearly showed the significance of solid-liquid interactions on the transport processes.