The spatially separated polypyrrole (PPy) bilayers composed of easily (PPy/Cl) and heavily permeable (PPy/dodecylsulfate) for anions component layers have been prepared by consecutive electrodeposition. The set-up of quasi-equilibrium potential E-r during conditioning in the solution of electrolyte and the potentiometric response of bilayers to ions and redox system in the test solution were studied. The short-term potentiometric response of the bilayer system is mainly determined by the outer layer. The participation of the inner layer is related with permeability of the outer layer and with sensitivity of the inner layer to the ions of the test solution, and leads to the dependence of the electrode potential on the duration of the bilayer system's exposure to the test solution. (C) 2004 Elsevier Ltd. All rights reserved.