Alpha-synuclein has recently been shown to be a major constituent of Lewy bodies in Parkinson's disease (PD). This observation led us to investigate the possibility that its detection in the cerebrospinal fluid (CSF) could be used as a marker for Lewy bodies in the central nervous system. In this study we determined the pattern of expression of alpha-synuclein in patients with sporadic Parkinson's disease (PD) and normal controls, using western immunoblotting in conjunction with an antibody that recognizes the carboxyl terminal of alpha-synuclein protein. The native 19 kDa band normally seen in brain homogenates was not found in the CSF of either parkinsonian patients or control subjects. However, a novel band was observed, which migrated at a position in the range of 42 kDa in CSF from both patients and controls. We conclude that alpha-synuclein cannot be used as a biomarker for Lewy bodies during life. However, further characterization of the 42 kDa protein may be of interest.