Cyclic voltammeiry has been used to investigate the role of the anions and the solution pH on the redox properties of polypyrrole electrosynthesised onto aluminium in alkaline solutions. The polymer film was characterised by SEM and IR spectroscopy. Moreover, the influence of the cathodic potential on the redox process was analysed for films formed in acid and alkaline solutions. The electrochemical response was compared with that obtained on vitreous carbon electrode. The differences in the shape and evolution of the voltantmograms during cycling have been explained by 4 different participation of the ions. The best redox activity of the polymer is obtained in NO3- due to the fact that this anion could limit the anodic dissolution of Al. The other anions analysed cannot be incorporated into the polymer matrix. As a consequence, the transport of OH- occurs, which provokes a significative Al dissolution. It is expected that the Al3+ ions generated during the electrodissolution are incorporated into the polymer in order to equilibrate the charge of the film. (C) 2004 Elsevier Ltd. All rights reserved.