Mixed vanadium and niobium tungsten oxide W-M-O (M = V, Nb) thin films were prepared by sol-gel from solution of tungsten oxychloride (WOCl4) and vanadium oxypropoxide (VO(OPr)(3)) or niobium oxybutoxide (Nb(OBun)(5)), respectively. The annealing temperature and time were optimized to 200 degreesC and 10 min. W-M-O (M = V, Nb) thin films were characterized by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. Evidence of different electrochemical behaviour is given where the presence of either vanadium or niobium leads to more neutral coloured films. (C) 2002 Elsevier Science B.V. All rights reserved.