IrOx films have been deposited on conducting transparent SnO2-coated glass substrates with sheet resistance of about 10 Omega/square by electrochemical oxidation of soluble iridium species in a basic aqueous medium. Before being efficient for deposition, the iridium-containing solutions have to be aged for a minimum time which is determined by UV-visible spectrophotometry. The IrOx films prepared following the procedure described show cyclic voltammograms similar to those of anodic iridium oxide films (AIROF)s grown on iridium surfaces, i.e. one or two redox systems depending on whether the pH of the electrolyte is below or above 5. The IrOx films could be completely dissolved in boiling hydrochloric acid solutions and consequently their iridium contents were very precisely determined. These analyses clearly showed that a total of two electrons/iridium are exchanged in a basic medium, i.e. one electron/iridium for each redox system as the charges involved in both systems are nearly the same. The optical properties of the IrOx films were monitored in situ under potential cycling. The more cathodic redox system was assigned to Ir(III)/Ir(IV), it exhibits an electrochromic behavior characterized by a complete transparency of the reduced state and a coloration factor approaching 18 cm(2) C-1 at 633 nm. On the other hand, no significant modulation of the transmitted signal at 633 nm was detected for the second redox system which was observed only in basic media and attributed to Ir(IV)/Ir(V).