A systematic study of the central and peripheral nervous systems in 3 cases of Parkinson's disease has demonstrated that Lewy bodies are present in 27 nuclei. Of these 20 nuclei (12 pigmented and 8 unpigmented) are involved in 2 or all 3 cases. It is noticed that the distribution of Lewy bodies in Parkinson's disease described here corresponds surprisingly well to that of monoamine (dopamine, noradrenaline and serotonin) cell bodies demonstrated in rats by the histochemical fluorescence method. This correlation is similar to that of Alzheimer's neurofibillary changes in postencephalitic Parkinsonism as described by Ishii. Inasmuch as these viewpoints are also in agreement with preciously reported biochemical data on Parkinsonism, it is suggested that Parkinsonism (idiopathic and postencephalitic) should represent a system degeneration of monoamine neuron systems.