The aim of this experimental study was to investigate the pathophysiological mechanisms involved in the acute effects of unilateral vibration on the digital circulation of healthy men. In the fingers of both hands of eight male subjects (age 23-47 years) who had never worked with vibrating tools, finger blood flow (FBF) and finger skin temperature (FST) in thermoneutral conditions, and the percentage change of finger systolic pressure (FSP %) after local cooling from 30 to 10 degrees C were measured. The right hand was exposed for 30 min to sinusoidal vibration with a frequency of 125 Hz and an acceleration of 87.5 m.s.-2r.m.s. A control condition consisted of exposure to the same static load (10 N) but without vibration. The measures of digital circulation were taken before exposure to vibration and static load and at 0, 30, 60, and 90 min after the end of each exposure. Exposure to static load caused no significant changes in FBF, FST, or FSP % in either the test right or the control left finger. Immediately after vibration, there was a temporary increase in FBF in the vibrated right finger, while the non-vibrated left finger exhibited no vasodilation. In both the vibrated and non-vibrated fingers, FBF and FST significantly reduced during the recovery time. A large inter-subject variability was observed for FBF and, to a lesser extent, for FST. In the vibrated right finger the decrease in blood flow was significantly related to cold-induced vasoconstriction in the digital vessels. Such a relation was not observed in the non-vibrated left finger. The results of this investigation suggest that acute vibration can disturb the function of digital vessels through two different and opposite mechanisms. Vibration appears to produce local vasodilation and to trigger a central sympathetic reflex vasoconstriction which can be recorded in the ipsilateral and the contralateral finger to vibration. Both local and central vasoconstrictor mechanisms are likely to be involved in the response to cold observed in the digital vessels of a vibrated finger.