Theoretical considerat ions and published research show that hitherto there is insufficient knowledge to establish whether it is necessary to include the impulsiveness of vibration in the assessment of health risk. Experiments have been carried out to examine whether there are different acute effects of impul se and nonimpulse vibration from hand-held tools on the hand -arm system. Ten male subjects were exposed to simulated Z vibration of different hand tool s under laboratory conditions. The human response was evaluated from measurements of (i) the biodynamic behavior of the hand-arm system (wrist, elbow), (ii) muscle activity (flexor carpi ulnaris, biceps, and triceps muscles), (iii) peripheral circulation (skin temperature), and (iv) perception. No general significant differences in the acute effects were found between shock-type vibration and nonimpulsive vibration for short duration exposure (up to 8 min) to vibration with the same frequency-weighted acceleration. It was concluded that no assessment of impulse vibration more stringent than that proposed by the International Organization for Stan dardization seems justified.