The production by the pyridine MPTP of a parkinsonian syndrome strikingly similar to the 'idiopathic' disorder, and the paucity of evidence supporting a hereditary or infectious etiology for Parkinson's disease (PD), have stimulated a search for environmental chemicals resembling MPTP that might cause PD. In support of this, descriptive epidemiological studies have found higher prevalences of PD in highly industrialized countries. In North America and Europe, early onset PD appears to be associated with rural residence. Factors associated with this include vegetable farming, well water drinking, wood pulp, paper and steel industries. In China, living in industrialized urban areas increases the risk of developing PD. Preliminary epidemiological evidence supports the hypothesis that environmental chemicals may be related to the development of PD, but specific chemicals and their specific mechanism(s) have not been identified.