Iron is increased in the substantia nigra of patients with Parkinson's disease, but the mechanism of its accumulation is unknown. We report the distribution of ferritin in the basal ganglia of hemiparkinsonian monkeys made by MPTP. We stereotactically injected MPTP unilaterally into the caudate nucleus of four monkeys, and the substantia nigra and the basal ganglia regions were stained for L-ferritin by an immunohistochemical method. The ferritin immuno-staining was most intense in the pallidum and the pars reticulata of the substantia nigra on both injected and non-injected sides. No significant difference was noted in the immunostaining for ferritin in the pars compacta of the substantia nigra between the injected and the non-injected side. Iron was increased in the pars compacta of the substantia nigra of this hemiparkinsonian monkeys in our previous study. Normal ferritin immunostaining on the injected side would indicate that iron accumulation is not related to altered metabolism of L-ferritin in this model.