Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to common marmosets causes a profound loss of dopamine and serotonin in the striatum. Additional daily systemic treatment of monkeys with the antioxidants ascorbic acid (100 mg/kg) and alpha-tocopherol (2,350 mg/kg) prior to, during and following administration of MPTP does not prevent the loss of dopamine and serotonin in the striatum, suggesting that these antioxidants are unable to protect dopaminergic neurones against neurotoxicity of MPTP.