The phenoxazine dye, Nile blue-A, has been electropolymerised on glassy carbon electrodes by potential cycling in phosphate buffer solution at pH 5.3, 6.0, and 7.0. The electrochemical behaviour was studied by cyclic voltammetry and electrochemical impedance spectroscopy in phosphate buffer solution, also adding KCl, NaCl, LiCl, K(2)SO(4), or Na(2)SO(4) in order to evaluate counterion effects. The redox process of the polymer film presented an equal number of electrons and protons and the studies with different electrolyte compositions showed influence of the cations and anions on the electrochemical behaviour. The best polymer electrochemical properties were obtained in pH 5.3 electrolyte for the polymer prepared at pH 6.0, important information for application in electrochemical sensors and biosensors. (C) 2011 Elsevier B.V. All rights reserved.