A longitudinal study was undertaken to evaluate changes in the prevalenceof vibration-induced white finger(VWF)among a population of Japanese state forestry workers during the period 1956-1980. The peak prevalence was 62.6%, determined for the cohort beginning chain-saw use in 1958-1959. Beginningwith the 1968-1969 cohort, the prevalence decreased significantly. During the study period the prevalences in this cohort were approximately 10, 20,30, and 40% after 2, 4, 7, and 12 years of exposure, respectively. The incidence increased gradually after 1960, and the peak value (5-6 %) was reached in 1966. The latency interval for the development of VWF averaged 6.4 (SO 3.7) years (6000 to 7000 h). The prevalence of VWF after the end of exposure fell to 50.2% in the cohort after more than 12 years of observation.