A high-performance liquid chromatographic procedure with electrochemical detection is described for the determination of urinary 8-hydroxy-2'-deoxyguanosine, a major oxidative DNA lesion induced by radical forming agents. A two-step solid-phase extraction procedure was followed for extracting 8-hydroxy-2'-deoxyguanosine from human urine and the analysis was performed on a RP-18 analytical column under isocratic conditions. The limit of detection of 8-hydroxy-2'-deoxyguanosine in urine was found to be 0.9 nM. The non-invasive assay provides an indirect measurement of oxidative DNA damage.