The electrochemical oxidation of 5-hydroxyindole-3-acetamide has been studied in phosphate buffers in the pH range 1.9-9.9 at a pyrolytic graphite electrode on the basis of voltammetric, spectral changes and product characterization. The oxidation of 5-hydroxyindole-3-acetamide occurred in a single well-defined peak. The initial electrode reaction has been proposed to involve a 1e(-), 1H(+) oxidation step at the -OH group to give the corresponding free radical, which resonates, at different positions in the ring. On the basis of these results, a probable oxidation route of 5-hydroxyindole-3-acetamide to various O-O and C-C linked hydroxylated dimers, which may be toxic in nature, has been proposed. It has been concluded that during the oxidation of 5-hydroxyindole-3-acetamide, hydrolysis also occurs to give corresponding acetic acid. (c) 2005 Elsevier B.V. All rights reserved.