With a microneurographic method, sympathetic nerve activity in the skin was recorded from median nerve fascicles of six patients with vibration-induced white finger and four age- and gender-matched normal subjects. At an ambient temperature of 15 degrees C the sympathetic nerve activity was greater in the patients than in the normal subjects. The burst activity was increased in all of the subjects during the water immersion test of the contralateral hand, but neither the increase in the mean burst number nor the mean area under the neurogram showed statistically significant group differences. Thus, although vasoconstrictive tone is greater in patients with vibration-induced white finger than in healthy subjects, no support could be found for the hypothesis that increased vascular tone is of prime importance for attacks of white finger in vibration-exposed subjects.