An intrastriatal injection with 18.8 nmoles of the neurotoxic agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced in rats a progressive parkinsonism characterized by a major loss of striatum dopamine (DA) levels and an increased turnover of this neurotransmitter 96 h after the administration. In addition, the intrastriatal administration of MPTP produced an alteration in various behavioral markers of motor activity. Loss of DA was accompanied by a significant decrease of reduced glutathione (GSH) and an increase in GSH oxidation in the striatum. When deprenyl (10 mg/kg) was i.p. administered 2 h before the intrastriatal injection of MPTP, DA, GSH, glutathione redox status and the indexes of motor activity were not altered. These results show that MPTP increases striatum oxidative stress leading to cellular and in vivo degenerative changes which are prevented by pretreatment with deprenyl.