Recently, a novel protein-interaction partner of alpha-synuclein, designated synphilin-1, is identified as a constituent of Lewy bodies (LB) in Parkinson's disease (PD) brains. To investigate an involvement of genetic variations of synphilin-1 in development of sporadic PD, a possible single nucleotide polymorphism (SNP) of T131C corresponding to a valine (Val) to alanine (Ala) substitution at codon 44 in exon 3 of the synphilin-1 gene was studied in a Japanese population of 55 patients with sporadic PD and 61 patients with non-PD by direct sequencing analysis. All 116 subjects showed a homozygosity of Val at codon 44 in the synphilin-1 gene, suggesting that this SNP is unlikely to affect genetic susceptibility to sporadic PD in the Japanese population.