A copper disc electrode working in alkaline solutions was demonstrated to act as a suitable amperometric sensor for ethanol determination at +0.6 V vs Ag \ AgCl. The participation of a freely soluble Cu(III) species in the electrocatalytic process involving the anodic oxidation of ethanol has been demonstrated by rotating ring-disc electrode voltammetry. The influence of the pretreatment potential on the anodic signal was investigated and a correlation with the morphology of the electrode surface characterized by energy dispersive X-ray spectroscopy (EDS) indicated that the Cu(III) species originated from the oxidation of a CuO layer. Ethanol measurements were performed in the amperometric mode at 0.6 V (vs Ag \ AgCl). The repeatability of the measurements for a 0.05% aqueous ethanol solution was estimated as 3%, and the detection and quantification limits were determined as 0.005% and 0.01%, respectively. Under the optimum experimental conditions, the amperometric sensor was used to monitor the concentration of ethanol in breath (BrAC), which was conveniently collected in a rubber air balloon (volume =3 l) and introduced to a 1 mot l(-1) NaOH working solution (volume = 10 ml). The sensor can measure a person's breath ethanol over the concentration range 0.26-130 ppm by operating it according to an established protocol, of which the analytical parameters are specified by the Brazilian legislation for BrAC measurements in drivers. The rate of ethanol degradation in the body was followed, and the results agree with predictions in the literature. (C) 2004 Elsevier B.V. All rights reserved.