The apparent electro-osmotic permeability, W, of three ion-exchange membranes has been obtained under different experimental conditions. The behaviour of W as a function of the current density, I, shows the following characteristics : (i) at sufficiently low values of I, the apparent electro-osmotic permeability decreases when the current density increases; (ii) at an intermediate values of I, a local maximum appears; and (iii) at the highest values of I, the apparent electro-osmotic permeability seems to approach a roughly constant value. The value of I at which the local maximum takes place is very close to the so-called limiting current density.