Neurofilament M, a major component of Lewy bodies, represents an interesting candidate in the pathogenesis of Parkinson's disease (PD). We performed detailed mutation analyses of the NF-M gene in 322 familial and sporadic PD patients. Two polymorphisms (Ala475Thr and Gly697Arg) occurred at similar frequencies in PD patients and controls. A Pro725Gln substitution and a deletion of valine in position 829 were identified in two PD patients. These substitutions affect residues of the NF-M protein that are highly conserved among different species. None of our patients carried the Gly336Ser substitution, which has been described in familial PD. Our results argue against a major role of NF-M in PD. However, rare variants of the NF-M gene may act as susceptibility factors for PD and functional analyses of the identified variations are warranted to decipher possible mechanisms in neurodegeneration.