Iron-induced oxidant stress has been implicated in the pathogenesis of Parkinson's disease. An increasing body of evidence now indicates that in Parkinson's disease the environment within the substantia nigra is conducive to the formation of cytotoxic free radicals and cell degeneration. Dopamine neurons may be particularly vulnerable because of the oxidative metabolism of dopamine and the potential of neuromelanin to promote the site-specific accumulation and reduction of iron. This hypothesis has attracted considerable attention because it opens the way for employing antioxidant strategies as possible neuroprotective treatment for Parkinson's disease. Although the concept is appealing, free radicals have not yet been proven to play a role in Parkinson's disease, and many important issues remain to be resolved before the oxidative hypothesis can ultimately be confirmed or refuted.