Electrochemical oxidation of indole, C8NH7, in a non-aqueous medium, such as a solution of LiClO4 or LiBF4, dissolved in acetonitrile, leads to the formation of polyindole, an air stable conducting polymer that exhibits electrochromic properties. The room temperature electrical conductivity, in the range 5 x 10(-3)-8 x 10(-2) S cm-1, depends slightly on the nature of the counterion.