In this study we investigated acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities and the molecular forms of these enzymes in the cerebrospinal fluid (CSF) of non-demented and demented Parkinsonian patients and in controls. The ratio of AChE to BChE activity was lower in the CSF of demented patients than in non-demented patients, although AChE and BChE activities and the molecular forms of AChE and BChE were the same in the different groups of patients. AChE activity in CSF did not vary according to the severity or duration of dementia associated with Parkinson's disease or with the disability stage of Parkinson's disease. BChE activity in CSF correlated with these clinical parameters, and patients with cerebral atrophy had higher BChE activity in CSF than those patients without atrophy. These alterations in the BChE activity of CSF may be related to gliosis which occurs in the degenerating brain tissue.