We measured plasma level of TM and ET-1 in vibration exposed patients. The results showed the plasma level of TM in vibration exposed patients was significantly higher than in normal controls. The present findings showed relatively wide damage of endothelial cells in the vascular bed of vibration-exposed patients. On the other hand, the mean level of ET-1 in these patients tended to be higher than in normal controls, though there was no difference. Further studies are necessary about the mechanism of endothelial damage in vibration syndrome patients and its contribution to peripheral circulatory disturbance of vibration syndrome including the role of ET-1.