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To investigate the dose-response relationship and the relationships among symptoms related to the vibration syndrome, 266 chain saw operators were examined. The subjects were classified into four groups according to total operating time (TOT): Group E1 (below 2,000 hrs, n = 39), Group E2 (2,000-5,000 hrs, n = 76), Group E3 (5,000-8,000 hrs, n = 51), and Group E4 (over 8,000 hrs, n = 100). The control group (Group O) consisted of 46 healthy subjects with very brief employment period as bush cleaners. The subjective symptoms and clinical findings were divided into four major symptom categories: circulatory disturbances, sensory disturbances, damage to muscles and joints, and general symptoms such as autonomic nerve disturbances. Each major symptom category was rated from 0 to 25 according to the severity of the symptoms observed (Table 2). The mean scores in the four major symptom categories were compared for the four TOT groups in order to study the dose-response relationship. The relationship among symptoms was investigated by cluster analysis for the four major symptom categories of all operators in each group and inferred from the significance of partial correlation coefficients between the two of the four major symptom categories calculated for each group. The mean scores in the four major categories showed a significant elevation with the increase in TOT. A dose-response relationship of the vibration syndrome was proved. Each major symptom category was aggravated, not independently, but in close correlation with the symptoms. The inter-symptom relationships of the vibration syndrome were confirmed. That is, very close correlations between circulatory disturbances and sensory disturbances and between sensory disturbances and damages to muscles and joints were demonstrated.