The electrochemical polymerization of EDOT on ITO from cesium cobaltabisdicarbollide acetonitrile solutions is accompanied by a reversible oxidation of the doping anion. It results in a p-doped polymer embedded with short-chain reduced oligomers, as proven by the material composition, morphology, electrochemical and spectroelectrochemical behaviour. The ratio between the number of EDOT molecules entrapped in the polymer vs. the oligomers is 0.88. This ratio was estimated from the doping level of the material considering that only the polymer can be doped. Its oxidation/reduction process takes place reversibly in the potential range -0.8/+0.7 V vs. SCE and is accompanied by cation exchange. The non-extrudable character of the doping anion was proven by electrochemical treatments designed to alter the material composition by ionic exchange followed by EDX or MALDI-TOF mass spectrometric analyses either of the material or of the 0.1 M LiClO4 acetonitrile solution in which the polymer oxidation/reduction had been performed. (c) 2006 Elsevier Ltd. All rights reserved.