The proto-oncogene bcl-2 is involved in the regulation of cell death and may be able to block apoptosis in neurons through reduced generation of reactive oxygen species (ROS). The bcl-2 product was measured for the first time in brain (caudate nucleus, putamen and cerebral cortex), ventricular cerebrospinal fluid (VCSF), and lumber CSF (LCSF) from control and parkinsonian patients by highly sensitive two-site sandwich enzyme-linked immunosorbent assay (ELISA). The concentrations of bcl-2 in the nigrostriatal dopaminergic regions were significantly higher in parkinsonian patients than those in controls, whereas this product in cerebral cortex showed no significant difference between parkinsonian and control subjects. Neither VCSF nor LCSF from control or parkinsonian subjects contained the bcl-2 product in the detectable amount (< 5 U/ml). Since oxidative stress may be involved in neurogenerative disorders, accumulation of bcl-2 may reflect a mechanism for counterbalancing ROS-mediated damage, or it might represent the impairment of bcl-2-dependent protection from ROS in parkinsonian brain.