Some conducting polyheterocycles prepared by electroinitiated polymerization as thin films on electrodes change color reversibly when they are electrochemically cycled. As an example, polypyrrole is synthetized in an oxidized form and may be reduced reversibly between 0 and - 0,7 volt vs SCE. The modified electrode change from brown to yellow during the cycling of the potential. Other colors may be obtained with other heterocycles. The electrochemical properties of some polyheterocycles have been determined and their characteristics-optical density, switching speed, ageing effects - are compared to those of other electrochromic organic materials.