Cyclic voltammetry with a platinum electrode of hydroquinone (BQH(2)) solutions in dichloromethane, containing tetrabutylammonium perchlorate supporting electrolyte, shows a sharp asymmetric irreversible oxidation peak at about -0.3 V (SCE). This feature is seen, in addition to the expected features in this system, when the cycle is extended to potentials more negative than -0.6 V (SCE). Cyclic voltammetry, in situ UV-vis and infrared spectroelectrochemistry have shown that hydroquinone anion (BQH(-)) is formed at negative potentials and this appears to arise via surface decomposition of hydroquinone to p-benzosemiquinone (BQH(-)) followed by reaction of BQH(.) with the p-benzoquinone radical anion (BQ(.-)). The sharp asymmetric peak in the cyclic voltammograms is due to oxidation of the hydroquinone anion in the insoluble tetrabutylammonium salt on the electrode surface. The oxidation of BQH(-) appears to occur via disproportionation of BQH(-) and leads to BQH, and p-benzoquinone (BQ) as the products.