Homovanillic acid (HVA), a major metabolite of dopamine, and 5-hydroxyindoleacetic acid (5HIAA), a major metabolite of serotonin, were measured in the lumbar CSF of 7 patients with Huntington's chorea, one patient with senile chorea, 5 patients with a clinical diagnosis of dentatorubropallidoluysian atrophy (DRPLA), 2 patients with essential myoclonus, 8 patients with Parkinson's disease and 10 normal subjects as controls. HVA levels in patients with DRPLA and Parkinson's disease were significantly lower than that of the controls. HVA levels were not altered in Huntington's chorea. One patient with senile chorea showed low HVA level. 5HIAA levels in Parkinson's disease were significantly lower than that of the controls. Two patients with essential myoclonus showed low 5HIAA levels. These results suggest that dopaminergic neurons in the central nervous system (CNS) might be impaired in DRPLA and Parkinson's disease, and that serotonergic neurons in the CNS might also be impaired in Parkinson's disease.