In five patients with cerebral manifestation of Wilson's disease, copper was measured in CSF, serum, urine and liver, and ceruloplasmin was determined in CSF and serum. CSF copper was found to be elevated in all cases, especially in the four examined before therapy. Two patients were followed up for a period of 3 years, while undergoing therapy with chelating substances. In case 1, the data and the clinical course are presented in detail: prior to therapy, the daily urinary copper excretion had been elevated, and this increased during the initial treatment stages. The serum copper concentration, which was already low, decreased quickly the during the initial stages of therapy, and remained at a low level during further treatment. In contrast to its level in serum, the copper level in the CSF was up to 3-fold the normal range and fell only very slowly as clinical symptoms improved. These findings suggest transport of copper from the CNS to the CSF. The copper concentration in CSF appears to be a valuable parameter for diagnosis and monitoring therapy in patients with cerebral manifestation of Wilson's disease.