The cathodic adsorptive electrochemical behavior of guanine in the presence of some metal ions at the static mercury drop electrode was investigated. A 1.0x10 - 3 mol l - 1 NaOH or a 2.0x10 - 2 mol l - 1 Hepes buffer at pH 8.0 solutions were used as supporting electrolytes. The reduction peak potential for guanine was found to be around -0.15 V, which is very close to the mercury reduction wave. A new peak appears at -0.60 V in the presence of copper or at -1.05 V in the presence of zinc. A square wave voltammetric procedure for electroanalytical determination of guanine in 2.0x10 - 2 mol l - 1 Hepes buffer at pH 8.0 containing 1.6x10 - 5 mol l - 1 of copper ions, was developed. An accumulation potential of -0.15 V during 270 s for the prior adsorption of guanine at the electrode surface was used. The response of the system was found to be linear in the range of guanine concentration from 6.62x10 - 8 to 1.32x10 - 7 mol l - 1 and the detection limit was 7.0x10 - 9 mol l - 1 . The influence of DNA bases such as adenine, cytosine and thymine was also examined. Cyclic voltammetry was used to characterize the interfacial and redox mechanism.