AbstractSmooth, adherent films of the electrically conducting polypyrrole formed on surfaces in contact with unstirred aqueous solutions containing the pyrrole monomer and the oxidant, FeCl3. Contradictory reports in the literature concerning the influence of HCl on the growth rate and electrical conductivity of polypyrrole grown in this manner prompted this study of the growth rate and conductivity of films. With no intentional addition of HCl, the growth rate of the films, measured using a quartz crystal microbalance, was fit to a simple second‐order model in which the rate was limited by the bulk depletion of reactants. The conductivity of the films was found to be about 1 S cm−1. Both the growth rate and the electrical conductivity initially increased with the deliberate addition of HCl to the solution. The conductivity was found to peak at a value about 20 S cm−1at an initial HCl concentration of 0.3M. At initial HCl concentration of 2Mor more, films could not be grown. © 1994 John Wiley&Son