In order to investigate the possible role of oxidative RNA damage in the pathogenesis of Parkinson's disease (PD), the concentrations of the oxidative stress marker 8-hydroxyguanosine (8-OHG) were measured in the cerebrospinal fluid (CSF) and the serum of patients with PD and control subjects. The concentration of 8-OHG in CSF in PD patients was approximately three-fold that in controls (P < 0.001). The concentration of 8-OHG in CSF decreased significantly with the duration of disease (r(s) = -0.46, P < 0.05). However, the concentration of 8-OHG in serum was not significantly altered in PD patients compared to that in controls. In addition, the concentration of 8-OHG in CSF showed no correlation with that in serum in both the controls and PD patients suggesting that the 8-OHG concentrations in the CSF do not reflect those in serum and may be probably reflect those in brain tissue. These in vivo findings suggest a possible role of 8-OHG and increased oxidative RNA damage in the early stage of the development of PD.