This paper shows that oligomers are retained inside the polymer film during the electrosynthesis of poly(3,4-ethylenedioxythiophene), PEDOT, ill aqeous media. The behavior of the electrochemically generated PEDOT film is highly dependent oil the presence of these oligomers. A detailed Study of the release of oligomers trapped in the PEDOT film has been carried Out using bidimensional spectroelectrochemistry (BSEC), spectroelctrochemistry quartz crystal microlalance (SEQCM) and scanning electrochemical microscopy (SECM), These multiresponse techniques have allowed LIS to determine when these EDOT oilgomers are released into Solution and to investigate their electrochromic properties. Mass Spectroscopy measurements revealed that most of these oligomers consist of four or six monomer. Units, Which seem to be the most stable species ill aqueous solution. (c) 2008 Elsevier Ltd. All rights reserved.