Finger skin blood flow was measured in 80 healthy subjects, using laser Doppler imaging during basal vasodilatation at a local temperature of 40 degrees C. The response to cooling of the contralateral hand at 15 degrees C was studied. A vasoconstriction index was calculated in all subjects and a nomogram was constructed, taking age into consideration. Compared with these normal subjects, four patients operated on with transthoracic endoscopic sympathectomy due to hand hyperhidrosis showed clearly attenuated responses. The results indicate that the test can be used to assess disturbances in the sympathetic regulation of the peripheral blood flow.