The electrocatalytic oxidation of guanine and DNA is demonstrated on a sol-gel coated carbon screen printed electrode modified with {MeReO(edt)}(2) using cyclic and differential pulse voltammetric techniques. An oxidation peak at 370 mV was found, but no corresponding reduction peaks could be detected in the negative scan, which indicates that the oxidation of guanine is completely irreversible process. The oxidation peak potentials are shifted to more negative values with increasing pH. The utility of applying the sensor for determination of guanine and ss-DNA were investigated. The linear ranges were 0.19-10.8 and 0.45-7.8 mu g ml(-1) for guanine and DNA, respectively. Detection limits of 0.1 and 0.32 mu g ml(-1) were obtained for guanine and ss-DNA, respectively. (c) 2007 Elsevier Ltd. All rights reserved.