Impedance plethysmography was used to measure bilateral blood flow in the forearms, hands, and digits of seven healthy male subjects. The objectives were to determine the degree of symmetry between right and left body segments and to quantify the extent of vasomotor change at ambient temperatures ranging from 10 degrees to 46 degrees C. The mean forearm blood flow index ranged from 3.9 ml/(100 ml . min) at 10 degrees C to 7.5 ml/(100 ml . min) at 46 degrees C. Mean hand blood flow indices increased from 1.6 ml/(100 ml . min) at 10 degrees C to 10.7 ml (100 ml . min) at 46 degrees C. Finger blood flow indices in the proximal and medial phalanges of the five digits ranged from less than 1.0 ml/(100 ml . min) at 10 degrees C to over 27.0 ml/(100 ml . min) at 46 degrees C. Although each subject demonstrated variations in right and left side blood flow during any selected experiment the grouped mean flow indices exhibited no statistically significant side dominance. These experiments quantify the vasomotor alterations in the upper extremities and indicate that the more distal body segments exhibit relatively larger vasomotor responses to changes in ambient temperature than do the more proximal body segments.