The influence of para-, ortho-, and meta-phenylenediamine (p-, o-, and m-PDA) additions on the electrochemical synthesis of polyaniline has been investigated by the use of cyclic voltametry. It has been found that small additions (1 and 5 mmol L-1) of PDA monomers influence significantly the polymerization rate. Whereas p-PDA increases the polymerization rate, the addition of o- or m-PDA slows it down. Therefore, a different number of potential cycling is necessary to obtain similar thickness of layers. The layers exhibit very different morphology, which changes from "spaghetti-like" for polyaniline to "sponge-like" for p-PDA, to "pebble-like" for o-PDA and to "cauliflower-like" for rn-PDA additions, respectively. The catalytic effect of the synthesized polymer layers has been tested. It has been found that all the layers exhibit catalytic effect in lowering the redox potential of hydroquinone/quinone tested reaction, but the rate of the electrocatalytic reaction varies depending on the PDA monomer added. (C) 2004 Wiley Periodicals, Inc.