The synthesis of polyaniline (PANI) thin films was made onto commercially available 5 cm x 5 cm polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. By depositing a gold frame previously to the electrochemical PANI synthesis, homogeneous electrochromic PANI layers were obtained. Complete flexible cells could then be built by using a transparent gel electrolyte and a simple PET/ITO counter-electrode. Branched poly(ethyleneimine) (BPEI)-H3PO4 and polymethylemethacrylate (PMMA)-PC-LiClO4 were both tested as electrolytes, but only the latter led to a non-degrading system when the device undergoes several switching potential steps. This flexible, middle-scale and inexpensive device enabled to get a 18% transmission contrast at 780 nm within 3 min. (C) 2004 Elsevier Ltd. All rights reserved.