By using square-wave voltammetry (SWV) and a boron-doped diamond electrode (BDDE), it was possible to develop and apply a new electroanalytical procedure for the determination and quantification of dimethomorph (DIM) with a quantification limit of 1.04 x 10(-6) Mol L-1. This voltammetric methodology was successfully applied to DIM determination in fresh grapes and red wine samples, with recovery values of 101.0 +/- 12.1% and 105.1 +/- 10.8% (95% confidence interval). Based on quantum-chemical studies and the data obtained by gas chromatography-mass spectrometry (GC-MS), it can be concluded that the site of oxidation of DIM is the non-aromatic double bond, and that the DIM electrooxidation reaction forms the (4-chlorophenyl)-(3,4-dimethoxyphenyl)methanone as a major product. (C) 2013 Elsevier Ltd. All rights reserved.