Thiophene-3-acetic acid has been polymerized in chloroform by a chemical method using FeCl3 as oxidant. The films were prepared casting the solubilized polymer on ITO electrodes and studied using cyclic voltammetry, chronoamperometry and spectroelectrochemistry. During the potential sweep, an electrochromic process is observed in which the film color changes from red to black. High electrochromic efficiency was observed for more than 600 cycles, although it decreases to 73% of the initial value. Until 264 cycles, the electrochromic efficiency at 750 nm is stable and the value is 242cm(2)c(-1). (C) 2004 Elsevier B.V. All rights reserved.