We studied 20 single nucleotide polymorphisms in 18 candidate genes for association with Parkinson's disease. We found that homozygosity for the V66M polymorphism of the brain-derived neurotrophic factor (BDNF) gene occurs more frequently in patients with Parkinson's disease than in unaffected controls (chi(2) = 5.46) and confirmed an association with the SI8Y polymorphism of the UCH-L1 gene. Our results provide genetic evidence supporting a role for BDNF in the pathogenesis of Parkinson's disease.