The radical scavenging ability of soluble conducting polymers has been examined using the DPPH assay in comparison with phenolic antioxidant compounds present in the diet. The reducing strength was also determined by voltammetry at a carbon electrode both in an aqueous pH 7.0 buffer, and in methanol as used for the DPPH assay. The conducting polymers were shown to be good reducing agents and effective scavengers of free radicals, with 2-4 DPPH radicals being reduced for each aniline or pyrrole unit on the polymer chains. The significance of this antioxidant capacity for the application of conducting polymers as biomaterials is considered. (C) 2003 Elsevier B.V. All rights reserved.