The electrochemical synthesis and the charging-discharging reactions of poly(3,4-ethylenedioxythiophene) (PEDOT) in two room-temperature ionic liquids, 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4) and 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF6) were studied with cyclic voltammetry, in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and by in situ UV-Vis spectroelectrochemistry. The structures of the films prepared in ionic liquids was compared to PEDOT films prepared in common organic media. The doping induced changes in absorption of the material both in the mid infrared and in the UV-Vis region were studied and interpreted according to spectra reported for PEDOT films prepared from common organic media. (C) 2004 Elsevier B.V. All rights reserved.