The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH 1.5) containing silver ions (0.02 g dm(-3) Ag+) and thermophilic bacteria (68 degrees C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S degrees and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.