The neuroprotective action of l-carnitine (LC) in the rat model of 3-nitropropionic acid (3-NPA)-induced mitochondrial dysfunction was examined. 3-NPA is known to produce decreases in neuronal ATP levels via inhibition of the succinate dehydrogenase (SDH) at complex II of the mitochondrial electron transport chain. SDH is involved in reactions of the Krebs cycle and oxidative phosphorylation, and its inhibition leads to both necrosis and apoptosis. LC enhances mitochondrial metabolism and, together with its acetylated form, acetyl-l-carnitine (ALC), via the LC-ALC-mediated transfer of acetyl groups, plays an important modulatory role in neurotransmitter signal transduction pathways and gene expression in neuronal cells. In the study described here, adult male Sprague-Dawley rats were injected with 3-NPA alone or treated with LC prior to 3-NPA administration. Pretreatment with LC totally prevented the 3-NPA-induced decrease in brain temperature measured using temperature probes implanted intracranially. It appears that the protective effects of LC against 3-NPA-induced neurotoxicity are achieved via compensatory enhancement of several pathways of mitochondrial energy metabolism. The results of this and previous studies conducted by our division in the 3-NPA model of mitochondrial dysfunction demonstrate that 3-NPA may be employed in vivo to evaluate enhancers of mitochondrial function that might exert neuroprotective effects.