The great majority of studies on tissue implantation in Parkinson's rat models have been performed. Recently the new rat model which is similar to clinical Parkinson's disease was developed. The characteristic feature of this model had the remaining dopaminergic neurons in substantia nigra(SN) after injection of 6-hydroxydopamine(6-OHDA). The investigators reported that the model was appropriate to studying the recently reported phenomenon of sprouting from host dopaminergic neurons following tissue implantation. But there has been no morphologic study of degeneration of dopaminergic neurons after the injection of the toxin. Authors investigated the changes of the dopamingic neurons in SN of selectively lesioned Parkinson's rat model. Acute changes of dopaminergic neurons in SN after injection of 6-OHDA, were pyknosis, decreased number and destruction of neurons and surrounding edema. Neurons distal to injection site were progressively destroyed and degenerated, and their nerve fibers were injured also. In chronic state, the number of dopaminergic neurons in right lesioned SN was decreased and about 10.2% of number of intact left SN. In right SN, glial cells were increased, scar reactions were noticed and large sized neuron was not visualized. Nerve fibers and neuronal processes of remaiming neurons were destroyed and their shape was irregular and their TH-IR reaction were decreased.