The results of chelation treatment of 137 patients presenting with neurological Wilson's disease are described, together with the more commonly observed toxic reactions to the various drugs employed. Fifty-seven patients made an excellent response to treatment and became symptom free. Thirty-six patients made a good recovery, but were left with some minor neurological deficit. Twenty-four patients had a poor response: although the disease process was arrested they were left more or less disabled. Twenty patients died: nine had little or no treatment, but 11 died despite apparently adequate chelation therapy. There was no obvious reason for this failure. The liver copper level was estimated in six of these patients: it was still significantly elevated in only one, but in all four in whom it was possible to make the determination, the concentration of copper in the basal ganglia was in excess of 45 μg/g wet weight. It was not apparent why adequate therapy failed to remove copper from the brains of these patients. There was no obvious clinical, histological or biochemical indicator of failure to respond to treatment. Initial deterioration before improvement was seen in 30 patients: the prognosis for a useful recovery was not necessarily worse than that in patients who did not show this phenomenon.