The purpose of this study was to determine whether some types of transcutaneous electrical nerve stimulation cause local vasodilation. The amount of vascular perfusion was monitored using telethermography to gauge the skin temperature of the area to which TENS was applied. We studied the effects of four different modalities of TENS (intensities of 1.5 and 3 times the sensory threshold and frequencies of 3 pulses per second [pps] and 100 pps), delivered through small and large electrodes (1.5 cm and 4 cm in diameter), on 10 healthy subjects. Stimulation at 3 times the sensory threshold produced local hyperthermia, which was maximal when a current of 100 pps was delivered through small electrodes. Because any physical or chemical effects of the current could be eliminated as causes of hyperthermia, the rise in skin temperature was considered to be a result of increased vascular perfusion. The results of the study demonstrate that some types of TENS cause local vasodilation. This effect may represent another mechanism by which such techniques provide pain relief, particularly in the treatment of myofascial syndromes.