Electrochemical probe beam deflection (EPBD) was used to investigate the behaviour of a silver electrode immersed in 0.1 M KClO4 solution containing various concentrations of KBr. The EPBD response was followed under potentiodynamic conditions and after potential steps. The EPBD transients were interpreted using standard models for the transport of ions in the diffusion layer. The AgBr(s) films formed after potential steps to mild anodic limits follow a nucleation-growth mechanism with progressive nucleation. The good agreement between the EPBD data obtained at intermediate anodic limits and linear diffusion models indicate that the film thickening was controlled by the diffusion of bromide ions from the bulk solution. EPBD experiments performed at high positive overpotentials and low bromide concentrations showed a net flux of ions away from the surface, suggesting that soluble Ag-(aq)(+) ions were produced through the porous AgBr(s) structure in these conditions. The EPBD curves obtained during the reduction of the film agreed well with a discontinuous diffusion model. However, EPBD experiments performed after film formation under high anodic limits and/or high bromide concentrations showed a complex pattern for the beam deflection during the reduction. In these cases, the EPBD signal was complicated by additional chemical process that occurred simultaneously with the reduction of the film. (C) 2003 Elsevier Ltd. All rights reserved.