Electrochromic films of NiOx and WOx were produced by the spray pyrolysis technique. The nickel-oxide-based coatings were obtained from an aqueous solution of nickel nitrate. Those obtained below 300° C did not show any diffraction peak when subjected to X-ray diffraction analysis, and those obtained above 400° C showed a diffraction pattern corresponding to cubic NiO. Films obtained below 300° C showed an electrochromic effect with an electrochromic efficiency of 30 cm2/C. Tungsten-oxide-based coatings were obtained from a solution of H2WO4 in aqueous ammonia. The films were grown at 150° C, and they showed a diffraction pattern corresponding to monoclinic WO3 when subjected to a post-heat treatment at 400° C during ten minutes. The WOx films showed a noticeable electrochromism under cation insertion, and presented an electrochromic efficiency of 42 cm2/C. Both as-deposited and heat-treated samples showed good electrochromism. © 1995.