The transport number of counterions in ion-exchange membranes (Nafion, Neosepta) has been predicted using the homogeneous and capillary models of transport. In the case of capillary model, two distributions of ions - described by the traditional and modified by Gur Boltzmann equations - have been applied. It has been found that the homogeneous model based on the experimental sorption and the capillary model, with the traditional Boltzmann equation, predict the transport number relatively well. The only exception is the anion-exchange membrane Neosepta AMI in HCl solutions, because of facilitated transport of protons through that membrane. It has been proved that the sorption given by the Boltzmann equation is always higher than that given by the modified Boltzmann equation and than the Donnan sorption. The modified Boltzmann equation, successful in predicting partition coefficient in Nafion 117 membrane equilibrated with H2SO4 solutions and salt mixture solutions, as reported by other authors, failed here.