The ability of aniline and polyaniline (PANI) samples to act as antioxidants using the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free-radical method are investigated by applying UV-VIS and ESR spectroscopy. The UV-VIS spectra of reaction mixtures in MeOH showed that PANI is more effective than aniline in eliminating the DPPH radicals by a factor of 5.8, while HCl-doped PANI was about 1.7 times more effective than PANI. A study of the kinetics of the reaction between DPPH and aniline showed that the reaction is first order with respect to DPPH and approximately second order with respect to aniline. The relationship between this and a previously proposed mechanism for this reaction is discussed. (C) 2003 Elsevier B.V. All rights reserved.