Antipsychotic agents have been widely used since their introduction in psychiatric practice. Their side effects have been well recognized. One side effect is the occurrence of tardive dykinesia. We reviewed the chemical anatomy of the neostriatum (caudate and putamen), and distinguished two major efferent systems (SI system and SII system). Firstly, we proposed the hypothesis that tardive dyskinesia is related to SII system hypofunction. The transmitter-receptor systems of the neostriatum were also disccussed, and the balance mechanism between them was stressed in the pathogenesis of tardive dyskinesia. We reviewed the relationship between tardive dyskinesia and drug induced Pakinsonism. CSF examination of tardive dyskinesia and drug induced Parkinsonism showed similar changes (i. e., increased HVA concentration). These two diseases might have a common prerequisite, and additional conditions might determine which disease develops. The receptoe blockade mechanism and supersensitivity seemed to play a key role in the appearance of the disease. To elucidate the pathogenesis of tardive dyskinesia and drug induced Parkinsonism further examination is critically needed
