The alteration of amino acids in cerebrospinal fluids (CSF) from 14 cases of Parkinson's disease, five cases of cerebellar degeneration and five cases of headache (control) was studied using high performance liquid chromatography. In patients with Parkinson's disease, it was found that the CSF level of GABA showed a significant decrease, while that of taurine had an increase. The degree of disability in Parkinson's disease and the decreased GABA levels had a positive correlation, especially at its advanced stages. In patients with cerebellar degeneration, it was also found that there was a significant decrease in CSF GABA. The present results suggest that the CSF level of GABA may be a good indicator of the severity of Parkinson's disease as well as the presence of cerebellar degeneration. Possible involvement of the increase of CSF taurine in the pathogenesis of Parkinson's disease is also suggested.