Guanine was electrochemically oxidised at polycrystalline gold electrodes. The potential for guanine oxidation at pH 7.4 was +690 mV versus Ag\AgCl when extrapolated to a scan rate of 3 mV s(-1). Kinetic analysis revealed the initial irreversible 2e(-) oxidation of guanine, achieved with fast scan cyclic voltammetry. At scan rates lower than 5 V s(-1), the 2e(-) oxidation changed to the extensive 4e(-) one. The initial 2e- oxidation of guanine, observed in the first scan, resulted in a quasi-reversible 1e(-) redox process of the oxidation product in the following scans, with a formal potential (E-o/) of +263 mV. This correlated well with the redox transformations of 8-oxo-7,8-dihydroguanine (8-oxoguanine, 8-oxoG). The kinetics of guanine oxidation on gold is discussed in detail within Laviron's approach and compared with that of 8-oxoG. (C) 2003 Elsevier Ltd. All rights reserved.