The effect of electric charge of ion-exchange resin and soil colloid on potential of ion-selective electrodes was investigated. It was found that the potential of ion-selective electrodes could be affected by the ion-exchange resin membrane or soil mass even when the sensitive membrane of the electrode was located at a distance of 2-3 mm from the latter. The potential was related to the kind of the electrode, the kind of the charged material that could induce such an effect, the concentration of the electrolyte, and the distance between the sensitive membrane of the electrode and the ion-exchange resin membrane or soil mass. It was suggested that the potential of ion-selective electrodes might be quite sensitive to minor changes in electric field or some of its derivative properties and that the effect was not only related to the electric charge of the ion-exchange resin or soil colloid, but also related to some electrochemical properties of the sensitive membrane of the electrode. In order to avoid possible errors caused by this long-range effect of electric charge of colloids on the potential of ion-selective electrodes in potentiometric measurements, the electrode should be located as far from the charged particles as possible.,