In a population of 566 forestry workers from nine lumber camps in Quebec and Ontario, 90 (27.9%) of 323 power saw operators complained of vibration white finger (VWF). The prevalence of reported white fingers was related to the period of work. From this population, 86 workers were selected for an objective clinical study. Modified finger-plethysmography gave the best discrimination between exposure groups. Radiograms of the hands suggested that bone cysts were more common among persons with VWF. The results of nerve conduction studies correlated with the effect of heavy muscular work rather than with the effect of vibration exposure. The octave-band accelerations of saws were measured during the cutting of 50 trees by 16 workers. Differences were found between saws, between sawyers, between cutting operations and between species of trees. The results of the study have implications for establishing standards.