An electrochemical sensor with soluble aldehyde dehydrogenase (EC 1.2.1.5) and diaphorase (EC 1.8.1.4) allowed the detection of acetaldehyde in a linear range from 1 to 500 mu M. The experimental conditions (0.1 M phosphate buffer, pH 7.5) were chosen to take into account the characteristics of the two enzymes. The NADH formed in the oxidation of acetaldehyde was enzymatically oxidized by diaphorase using hexacyanoferrate (III), and the hexacyanoferrate (II) produced was electrochemically oxidized at a potential of 81 mV applied between two platinum electrodes. Validation of the assay was made on wine, beer, and cider by comparison with a standard spectrophotometric method.