Polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) powders were prepared using various molar ratios of ammonium persulfate (APS) to their respective monomers. The antioxidant properties of these polymers were investigated through their reaction with the stable and intensely coloured DPPH radical. The DPPH scavenging activity was higher for PPy versus PEDOT, and decreased for both conducting polymers as the level of APS oxidant used in their formation was raised. The conductivity of the resulting polymers also decreased as more APS was used, which was related to overoxidation of the polymers seen by changes in FTIR bands. (c) 2007 Elsevier B.V. All rights reserved.