Voltammetry of dopamine at overoxidised polyindole-modified electrodes was investigated. The effects of the overoxidised polyindole film thickness, preconcentration and electrode fouling, as well as detection of dopamine in mixtures with ascorbic acid, were investigated. Although sensitivity was lower than at an uncoated electrode, selectivity was achieved at the modified electrode due to the discriminatory property of the overoxidised polyindole against ascorbate, an anion under the conditions of this study. (C) 2004 Elsevier Ltd. All rights reserved.