DJ-1 was initially identified as a novel oncogene and has recently been found to be a causative gene for a familial form of Parkinson's disease (PD), viz, PARK7. Cysteine residue at position 106 (Cys-106) in DJ-1 was found to be oxidized preferentially under oxidative stress. In the present study, we developed specific antibodies against Cys-106-oxidized DJ-1 using baculovirus particles displaying the surface glycoprotein gp64-fusion protein as the immunizing agent. Western blot analysis combined with two-dimensional gel electrophoresis revealed that these antibodies specifically recognized oxidized DJ-1. Furthermore, we developed a competitive enzyme-linked immunosorbent assay (ELISA) for detecting oxidized DJ-1 and measured blood levels of oxidized DJ-1 in PD patients (n=15). It was observed that the levels of oxidized DJ-1 in erythrocytes of unmedicated PD patients were markedly higher without overlap than those of medicated PD patients and healthy subjects. No significant difference was observed in DJ-1 levels between mediated and unmediated PD patient. These results suggest the oxidative modification of DJ-1 in PD patients and the potential application of the antibody for diagnosis of PD at early-stage.