Less than 10 years have passed since the discovery that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is capable of producing parkinsonism in both humans and non-human primates. In that time, there has been considerable interest in the possibility that the pathogenesis of idiopathic Parkinson's disease (PD) might involve a process analogous to that of MPTP toxicity. One hypothesis holds that PD might arise, at least in part, from exposure to an MPTP-like environmental toxin. Rapid progress has been made towards elucidating the precise mechanism by which MPTP exerts toxicity, and clarifying the relationship of MPTP toxicity to idiopathic PD. The goal of these efforts is to develop a therapy that inhibits the underlying disease process in PD.