Sympathetic effects of manual and electrical acupuncture of the Tsusanli knee point were evaluated by thermography in 19 normal subjects under the same procedure used in a previous study using the Hoku hand point. A generalized long-lasting warming (sympathetic inhibition) effect was observed under manual and electrical acupuncture of the Tsusanli point. In addition, a segmentally related short-lasting cooling (sympathetic activation) effect occurred with Tsusanli electrical acupuncture only. The warming effect is consistent with the results of the Hoku study and appears to be a central sympathetic inhibition evoked by acupuncture. The cooling effect was segmentally related to the acupuncture site in both studies. This cooling effect most likely reflects a segmental activation of vasomotor spinal reflexes and not a general emotional arousal. These sympathetic mechanisms may be functionally correlated with central and peripheral mechanisms of acupuncture analgesia.