OBJECTIVES: Manganese is cytotoxic to the central nervous system including basal ganglia. Its toxic mechanism is related to oxidative stress, mediated by toxic free radicals but is specultives. In the present study, we have investigated to manifest apoptosis in manganese-induced cytotoxicity in primary neuronal cell culture of rat basal ganglia. METHOD: To detect apoptotic neuronal cells were stained by the terminal deoxynu-cleotide(TdT)-mediated dUTP nick end-labelling(TUNEL) method and apoptotic changes in nuclei of neurons were observed by electron microscopy. RESULTS: We showed that TUNEL immunostain showed brownish signal in the nuclei of apoptotic cells and the proportions of apoptotic cells in Manganese treatment groups were more higher than controls. On transmission electron microscopy, there were chromatine condensation with margination toward nuclear membrane and condensation of cytoplasm in the treated with luM MnC1, for 48 hours in a basal ganglia neurons. Apoptotic bodies were found and consisted of semilunar-like condensed nuclei with relatively intact cytoplasmic organelles. CONCLUSIONS: Apoptosis appears to be one mechanism in the manganese-induced neuronal cell death. Manganese intoxication is a convenient model for apoptosis study.