Direct forearm blood flow measurements showed that the threshold for vasodilation is shifted to a higher core temperature and that the slope describing the relationship between skin blood flow and core temperature is reduced during submaximum exercise in comparison with supine resting conditions. These changes in skin blood flow characteristics have been shown to be proportionately related to work load in at least one study, but not in others. With heavy exercise, indirect evidence was obtained for the elicitation of vasoconstriction after body core temperature had attained a level of 39 degrees C; this caused a dramatic rise of T core to above 40 degrees C. In other studies, such terminal vasoconstriction was not observed; the subjects stopped exercising (75 percent VO2 max), independently of its duration, when rectal temperature had reached about 39 degrees C. Such inconsistent results in regard to the importance of extrathermal control of skin blood flow may be traced to variations in the motivational and emotional state; moreover, a phenomenon described as "short-term adaptation" may be responsible for some discrepant results. In conclusion, there is evidence for the concept that blood pressure control by peripheral vasoconstriction may have, under certain circumstances, preference over the demands of temperature regulation.