In July 1957, at the First International Congress of Neurological Sciences in Brussels, J. N. Cumings summarized the state of our knowledge on the biochemistry of basal ganglia diseases in one sentence: "The biochemical pathologist has so far been of practical assistance to the clinical neurologist and to the patient in only one of the group of extrapyramidal disorders, namely hepato-lenticular degeneration."1 Progress in the understanding of Wilson's disease, which had been hesitant for many years,2has been rapid and constant since 1957 but very little has been added to the biochemistry of the other basal ganglia diseases. For that reason we feel that some recent developments in this field must be brought to the attention of neurologists. As is well known, biochemical changes in mental disease, especially alterations in catechol-amine and serotonin metabolism, are becoming increasingly important, and it may be that the present findings will give