We report on chemical in situ deposition of poly(o-anisidine) and polyaniline on bare and thiol-modified gold. It is shown that the process of o-anisidine polymerization is initiated on the metal surface and in consequence it is very sensitive to modifications of the coating substrate. Polyaniline deposited under the same conditions does not reveal such sensitivity as the polymer is forming in the polymerization solution and is subsequently physisorbed on the surface. Thus, the substrate itself has little effect on the polymer deposition rate. The large differences in deposition rates of poly(o-anisidine) make this material promising in preparation of polymeric patterns using lithographic methods. (C) 2005 Elsevier Ltd. All rights reserved.