This paper presents first a set of experimental data on the measurements of the ionic fluxes through a cation-exchange membrane separating two electrolyte solutions with the same concentration, the same co-ion but different counter-ions (bi-ionic system). Then these results are compared with the theoretical predictions given by the resolution of the corrected Nernst-Planck's equation in the cases of the homogeneous and heterogeneous models of ion-exchange membranes. A good agreement between the experimental results and the computed values is observed only in the case of the heterogeneous model. This confrontation confirms (i) the existence of three concentration domains: low, medium and high concentrations, corresponding respectively to a complete diffusion boundary layers (DBLs) control, a mixed control and a complete membrane control of the inter-diffusion process; (ii) the homogeneous model, even if it is convenient for a good interpretation of the bi-ionic potential (BIP) results, can not explain quantitatively the trans-membrane ionic fluxes, which are extensive quantities; and (iii) the bi-phasic model gives the best predictions for both fluxes and BIPs.