In order to propose new stable immunosensors with potential applications in the phosphate buffer saline solution (aqueous solution at pH 7.2 containing 0.13 M NaCl and 0.05 M potassium phosphate), poly(pyrrole) films with various counter-anions (chloride, benzene sulfonate, benzene disulfonate and dihydroxybenzene disulfonate) were prepared by electrooxidation of pyrrole in aqueous solutions. The aim of this work was to determine the ion exchange properties of these poly(pyrrole) films during redox transformations, these properties being intimately connected to the probing characteristics of the sensors. To investigate the system thoroughly, the behaviour of the films was studied successively in the three following aqueous media: firstly 0.13 M NaCl, then 0.05 M sodium phosphate at pH 7.2 and finally 0.13 M NaCl + 0.05 M sodium phosphate at pH 7.2. This study was carried out by coupling a cyclic voltammetry technique to an optical method which allows the probing of the ionic fluxes in the diffusion layer of an electroactive material (probe beam deflection method). The results show that among all synthesized poly(pyrrole)s, only those with Cl- and dihydroxybenzene disulfonate as counter-anions have reversible redox changes in the phosphate buffer saline solution. In the poly(pyrrole) films with Cl- counter-anions, it is shown that the Cl- anion is the main ion exchanged during redox changes. On the other hand, mainly cationic motion has been found in the poly(pyrrole) films with dihydroxybenzene disulfonate anions. (C) 2000 Elsevier Science Ltd. All rights reserved.