The administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice was found to cause a long-lasting depletion of striatal dopamine concentrations, but did not alter striatal serotonin concentrations. The concomitant administration of ascorbic acid attenuated this MPTP-induced dopamine depletion. These observations are discussed in reference to the possible mechanisms through which MPTP exerts its neurotoxic actions on dopaminergic neurons.