Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons and the presence of intracytoplasmic inclusions (Lewy bodies). Iron, which is elevated in the substantia nigra of PD patients, seems to be of pivotal importance, because of its capacity to enhance the amplification of reactive oxygen species. As iron enters and exits the brain via transport proteins in the blood-brain barrier (BBB), these proteins may represent candidates for a genetic susceptibility to PD. P-glycoprotein (P-gp) is one important efflux pump in the BBB. There is evidence that the function of P-gp is impaired in PD patients. In the current study we examined ten coding single nucleotide polymorphisms in the multidrug resistance gene 1 (MDR1) encoding P-gp to assess whether certain genotypes are associated with PD. However, genotyping of 300 PD patients and 302 healthy controls did not reveal a significant association between coding MDR1 gene polymorphisms and PD.