Intrastriatal injection of the reversible succinate dehydrogenase inhibitor malonate produces both energy depletion and striatal lesions similar to that seen in cerebral ischemia and Huntington's disease. The mechanisms of neuronal cell death involve secondary excitotoxicity and the generation of reactive oxygen species. Here, we investigated the effects of dopamine on malonate-induced generation of hydroxyl radicals and striatal lesion volumes. Using in vivo microdialysis, we found that malonate induced a 94-fold increase in extracellular striatal dopamine concentrations. This was paralleled by an increase in the generation of hydroxyl radicals. Prior unilateral lesioning of the nigrostriatal dopaminergic pathway by focal injection of 6-hydroxydopamine blocked the malonate-induced increase in dopamine concentrations and the generation of hydroxyl radicals and attenuated the lesion volume. In contrast, the NMDA receptor antagonist MK-801 attenuated malonate-induced lesion volumes but did not block the generation of hydroxyl radicals. Thus, the dopaminergic and glutamatergic pathways are essential in the pathogenesis of malonate-induced striatal lesions. Our results suggest that the malonate-induced release of dopamine but not NMDA receptor activation mediates hydroxyl radical formation.