The influence of a catalytic amount (e.g. 0.1%) of 2.2'-bithiophene on the electrochemical polymerization of 3-bromothiophene has been investigated. The presence of bithiophene in the polymerization medium decreases the minimum potential required for poly(3-bromothiophene) deposition, and increases the polymerization rate at a given potential. However, the electrochemical generation of 3-bromothiophene cation radicals is required for poly(3-bromothiophene) formation, indicating that radical-monomer coupling is not a significant polymerization pathway. The main role of bithiophene in promoting poly(3-bromothiophene) deposition appears to be as a nucleation initiator. A negligible quantity of bithiophene is incorporated into the polymer.