In terms of neurotransmitter, most of the clinical data for Parkinsonism came from studies of idiopathic Parkinson's disease while the data of CO related Parkinsonism were limited to case reports. From neuropathology studies in idiopathic Parkinson's disease, dopamine deficits and decreased in monoamine transporters were observed well before the development of clinical features. Although there is linkage between CO related Parkinsonism and dopamine deficits, patients with CO intoxication had poor response to levodopa. The observation suggested the critical networks and neurotransmitters were still not well understood.