The cerebrospinal-fluid copper concentration, measured by electrothermal atomisation/atomic absorption spectrophotometry, was significantly higher in 24 patients with untreated, idiopathic Parkinson's disease than in a control population of 34 patients (p less than 0.001). The difference in the in-vitro capacity of copper to damage DNA, measured by the phenanthroline assay was even greater. The high phenanthroline-copper concentration correlated with disease severity (p = 0.02) and with the rate of progression of disease (p less than 0.05). A possible role is suggested for copper-catalysed oxidative mechanisms in the pathogenesis of Parkinson's disease.