The electrochemical response of zeolite-modified carbon paste electrodes (ZMCPEs) has been exploited to plot the normalised ion-exchange isotherm of methylviologen and sodium in zeolite Y. Results observed from the proposed methodology agree well with those obtained using the conventional procedure. Selectivity was very high for the large organic divalent cation over sodium species. but the degree of exchange of methylviologen did not exceed 64%. Electrochemistry of ZMCPEs allows the in situ quantitative determination of methylviologen in the zeolite phase, without significant modification in the solution-phase concentrations. so that the ion-exchange isotherm can be plotted very rapidly and without any other chemical analysis.