Copolymers of aniline and thiophene prepared electrochemically were studied with elemental analysis, cyclic voltammetry, in situ UV-vis spectroscopy and conductivity measurements. The influence of the feed ratio, the mode and electrode potential of deposition and the composition of the deposition solution were studied in order to verify the obtained polymers as true copolymers or merely composites or mixtures. (C) 2004 Elsevier Ltd. All rights reserved.