The performances of all solid state potassium selective electrodes with polypyrrole film as solid internal contact were evaluated. Potentiometric measurements revealed near Nernstian responses close to values already given in the literature for classic ISEs. In addition, ac-electrogravimetry was used in order to study the ions and solvent motions at the membrane/electrolyte interface. We have found that potassium ions enter the selective membrane firstly but solvent molecules and anions are also participating in the phenomenon. (c) 2005 Elsevier Ltd. All rights reserved.