This article discusses the results for the development of a nanogold-particle/polyaniline-modified glassy carbon electrode for the detection of arsenic(III) in water. A thin polyaniline film was electropolymerized onto a glassy carbon electrode. The gold nanoparticle was then deposited onto the polyaniline-coated glassy carbon electrode via potential step electrolysis from 1.1 to 0 V versus Ag/AgCI/NaCl (saturated) 1for 45s from a 0.5M H2SO4 solution containing 0.1 mM NaAuCl4 in the absence and presence of a 0.1 mM KI additive. The surface of the modified electrode was examined with scanning electron microscopy. Cyclic and anodic stripping voltam-metry of arsenic(III) was performed on the modified electrode. The thus modified nanogold-particle/polyaniline-modified glassy carbon electrode prepared in the presence of the I-(KI) additive showed a high sensitivity in detecting arsenic(III) in water, and with stripping voltammetry, a limit of detection of 0.4 ppb arsenic was obtained, which is much lower than the arsenic guideline limit of the World Health Organization. (c) 2007 Wiley Periodicals, Inc. J Appl Polyrn Sci 104: 1306-1311, 2007.