The electrochemistry of 3,4-dibenzyl-2,5-dimethylthiophene-S-oxide was investigated as well as its interaction with dsDNA. The electrochemical study of the thiophene-S-oxide was performed at different pH values, in a mixed solvent and by solid state voltammetry, and showed that the molecule is reduced at a very negative potential, and the reduction is pH dependent. A glassy carbon electrode modified with a thick thiophene-S-oxide + dsDNA mixture was used to study the interaction of thiophene-S-oxide in situ with dsDNA at a charged interface. The experimental results give strong evidence that the reduced thiophene-S-oxide interacts with dsDNA causing damage with possible strand break and that the thiophene-S-oxide adduct formed with dsDNA can still undergo reduction. (C) 2003 Elsevier Science B.V. All rights reserved.