The abundance of cellular superoxide dismutase (Mn-SOD) was examined immunocytochemically in different regions of the brain of Long-Evans Cinnamon (LEC) rats at 4 and 50 weeks of age. When all animals develop chronic hepatitis, the substantia nigra and striatum showed a marked increase in Mn-SOD immunoreactivity versus Long-Evans agouti (LEA) rats of the same age. Mn-SOD was localized predominantly in dopaminergic neurons. The elevation of Mn-SOD level in the dopaminergic neurons of LEC rats may reflect the oxidative stress caused by copper accumulation in this brain area. Our data suggest that LEC rats may contribute to the mechanistic study of neurological manifestations in nigro-striatal dopaminergic system of Wilson's disease.