The clinical courses, cerebrospinal fluid (CSF) and serum copper concentrations and urinary copper excretions under different schemes of drug treatment in four patients with cerebral manifestations of Wilson's disease were monitored over 6-11 years. CSF copper concentration measurements were performed from the beginning of therapy onwards in three patients and from 16 months after initial treatment onwards in the fourth. CSF copper levels decreased slowly over the years in parallel with clinical improvements, and increased in one patient who interrupted therapy for 2 years. These findings confirm our hypothesis that the concentration of copper in the CSF is a valuable quantitative parameter reflecting the normalization of copper in the brain. Copper measurements during phases of initial neurological deterioration in two patients receiving D-penicillamine, and in one patient receiving D-penicillamine and zinc sulphate, revealed decreased free serum copper and CSF copper levels.