The disease due to mechanical vibrations has been regarded as that showing Raynaud's phe-nomenon. The authors have observed that the patients with vibration disease have symptoms of the central nervous disturbance. The purpose of this study was to clarify evidences of the disturb-ance of the central nervous system caused by mechanical vibrations.Clinical features and laboratory findings of 60 patients hospitalized with vibration disease were analysed, 50 of them being chain saw operators in the forest, and 10 jack hammer operators in the rock. The average age was 47.4 years (range, 33-67) in the former and 51. 6 years (range, 37-60) in the later. The operators of chain saw and jack hammer had worked for 2 to 16 years (average 9.8) and for 4 to 7.2 years (average 5.8), respectively. The classification of severity by Andreeva-Galanina's criteria showed one patient in Grade II, 55 in Grade III and 4 in Grade IV.Incidences of subjective symptoms of peripheral functions such as Raynaud's phenomenon, . numbness, pain, cold sensation or stiffness of fingers ; pain on elbows and neck ; stiffness of shoul-der and lumbago were almost the same as those reported by many investigators. However, there were higher incidences in the complaints induced by the central nervous disturbance. These com-plaints were heavy feeling of head, headache, severe sleeplessness, early morning wakefulness, disturbance of memory, depressive feeling, palmar sweating and impotence. The incidence of each of these complaints ranged from 50% to 90%. Moreover, there were strikingly characteristic pat-terns in electroencephalograms, i. e., fast waves of twenty five Hz with or without spindle form were found in the frontal or pariental poles. The incidence of the fast waves was in proportion to the severity of the disease, waves appearing sporadically or continuously. In the Grade IV, however, the fast waves disappeared perfectly and flat EEG patterns appeared. The spindle-formed fast waves were disfigured to the non-spindle form by potent treatments. On discharge of the patient fast waves of the non-spindle form disappeared as well. Amplitudes of the fast waves of spindle and non-spindle forms were 50 to 60 μV, and 30 μV, respectively.In conclusion, the vibration disease is considered to be a systemic disease. Namely, the me-chanical vibration impaires not only peripheral circulatory and nervous functions and bones and joints, but also the central nervous system. Clinical symptoms have been relieved by treatments.In a certain degree of severity, disturbances caused by mechanical vibrations are reversible and functional. The clinical symptoms of the vibration disease are mainly induced by the disturbance of nervous, circulatory and hormonal systems and bones and joints. These can be divided into peripheral and central features.