Abstract: ObjectiveTo observe the microstructure of the substantia nigra of mice chronically into xicated with Cd.MethodsLight microscopy and trasmission electorn microscopy were used.The TH-positive neurons in the substantia nigra were analyzed with morphometric technique.Results(1)Most neurons were deg enerated.The nuclei appeared pycnosis and defor matio n.The heterochro matins were increased and mig rated to the mar ginal zone of the nuclei.The nissl bodies(rough surfaced endoplasmic reticulum and free ribosome)and other org anelles in the parikaryon obvously were decreased.(2)Afew necro tic neurons were found.The nuclearenvelopes were broken and the nuclei were dissolved.The Nissl bodies and other organelles in the parikaryon were disappeared.(3)The quantity of dopamine neurons and the dopamine producted by them were decreased.(4)There were the softening focuses in the substantia nigra.The boundary of the focuses were clear.Some neurons were dissolved and some neurons were deg enerated in the focuses.(5)The inflammation were seen in the substantia nigra.Numberous limphocytes were appeared in the inflammatory areas.The lymphocytes fo rmed an sheath in the periphery of small blood vessel.These findings indicated that the substantia nigra is a target of chronic Cd toxicity and alterations of the micr ostructure of the substantia nigra by chronic Cd toxicity (especially the quantity of dopamine neurons and the dopamine producted by them were decreased)are similar to the patholog ical charateristics of Parkinson's disease.ConclusionCadmium would be one of the factors induced Parkinson's disease.