Although the ultimate origin and role of mitochondrial pathology in Parkinson's disease (PD) remains controversial, accumulating data suggest that mitochondrial dysfunction is genetic and plays an important role in neurodegeneration. PD mitochondria display abnormal electron transport chain activity, increased reactive oxygen species generation, and abnormal calcium handling. These abnormalities arise, at least in part, from information encoded by mitochondrial DNA. These processes are implicated in current models of neuronal death and validate ongoing efforts to develop mitochondrial-level pharmacologic interventions for the treatment of this disease. (C) 1999 Wiley-Liss, Inc.