The levels of copper and ceruloplasmin in the cerebrospinal fluid (CSF) of patients with Wilson disease were investigated. Ceruloplasmin concentrations in the CSF of all patients were almost the same but were lower than those of the controls. CSF copper concentrations in patients without neurologic signs were within the normal range, 22 +/- 6 ng/ml. In contrast, CSF copper concentrations in patients with neurologic signs (69-98 ng/ml) were significantly higher than the normal levels before and at the beginning of the treatment with D-penicillamine; it gradually decreased in response to treatment. These results suggest that the appearance of neurologic manifestations in Wilson disease is not related to the CSF ceruloplasmin concentration. The CSF copper concentration in this disease appears to reflect copper accumulation in the brain and may be useful as a marker for monitoring therapy.