A group of manual workers (N=18) who operate low-vibration power tools (|a[inf hw]|[inf max]<2 m s[sup -2]) has been examined for objective evidence of work-related changes in hand and arm function. The subjects were drawn from and selected to be representative of a cohort of chain saw operators (N=124) whose health has been followed prospectively, 30% of whom reported experiencing numbness in the upper extremities. A method for detecting a statistically sufficient change in tactile acuity from measurements of mechanoreceptor-specific vibrotactile perception thresholds conducted over a 5-yr interval has been developed, together with any shift in acuity from the value occurring in healthy persons. A progressive deterioration in acuity was found in 12/36 hands, which is predicted to result in abnormal acuity in 39% of the group after a further 5 yr of work. The subjects predicted to be most severely affected currently exhibit reduced hand grip, and reduced hand and arm strength.