The attempt to reduce the number of coefficients in the transport equations of linear non-equilibrium thermodynamics (LNET) has been presented. By neglecting some of the interactions between transported species the equations relating the independent experimental transport quantities have been derived. These relations have been tested using the experimental data determined for the Nafion and Neosepta membranes in contact with various 1: 1 electrolytes. Generally, better predictions of the transport quantities have been obtained for the more swollen Nafion membrane. The most reliable results for the Nation membrane have been found assuming no counterion-coion interactions (r(12) = 0). This assumption simplifies the LNET equations to the extended Nernst-Planck equation with the convection factor. The neglecting of other interactions can lead to satisfactory results only in some certain cases. It has been demonstrated that the Monte Carlo method can help in obtaining more reliable results. (c) 2007 Elsevier B.V. All rights reserved.