Na-form cation-exchange resin particles were filled between a pair of platinum electrodes, across which an alternating current was applied in order to measure the impedance of the cell. It was found that a discontinuous change occurred in the relationship between the impedance and the measurement frequency, when the impedance measurement was carried out under circulation of pure water. Hysteresis in the impedance measurement was clearly observed by reversing the direction of the frequency change. As the impedance measurements were carried out by applying alternating currents, this system would be nonequilibrium far from equilibrium in a range of lower frequencies. Until now, it has been shown that there is always a positive feedback mechanism working in the hysteresis system, and therefore, we propose in this article a model system where the positive feedback is caused by autocatalytic water dissociation. Theoretical considerations were carried out based on the model, and a fairly good coincidence between the theoretical and the observed impedances were confirmed. (c) 2005 Elsevier B.V. All rights reserved.