The electrosynthesis of polythiophene (PTh), polyaniline (PANI) and polypyrrole (PPy) films modified by dispersion of Pt or Pt + Pb and its employment in the electrocatalytic oxidation of HCOOH are studied and compared. The influence of parameters such as polymer film thickness, the number of dispersed Pt particles, the amount of Pb deposited and the presence of Pb2+ in the electrolyte on the electrooxidation of HCOOH is investigated. Electrode systems including the polymer and a mixture of Pt and Pb particles show a better electrocatalytic activity than electrodes having a polymer-Pt combination or bulk Pt electrodes. Furthermore, during the electrooxidation of HCOOH using polymer-(Pt + Pb) electrodes the presence of fewer poisoning species is observed, indicating that the role of Pb in these electrode systems is in agreement with the Pb adatom effect observed when bulk Pt electrodes are used. However, the presence of Pb(rr) in the electrolyte is not required for the PTh-(Pt + Pb) electrode system and, in addition, a better electrocatalytic effect is obtained in this case. With application of an appropriate E/t program the activity is unchanged over a long time.