The purpose of this study was to investigate the effect of the De-Qi sensations of acupuncture (sourness-distension and distension-numbness) stimulation. Fifty-two healthy medical student volunteers were given acupuncture at the Hoku (LI-4) acupoint as they were resting. During a test that lasted 30 minutes, their skin blood flow was measured at the Quchi (LI-11) acupoint and their palm temperature was measured. Our results indicated that acupuncture increased blood flow when the De-Qi sensation occurred. If the needle was twirled a few minutes thereafter and the De-Qi feeling again occurred, the same blood flow increase was seen again. If the needle was not twirled, but the test person felt soreness, numbness and heat sensation within a few minutes after needle insertion, the same blood flow increase was also seen. After acupuncture, Quchi did not show continuous increase of blood flow as did Hoku. Hoku acupuncture also increased palm temperature suggesting that the blood flow increased from cutaneous vessel vasodilation. In conclusion, when the test person felt the sore and numb De-Qi sensation, there was an increase of blood flow at the acupuncture points. Thus, our results suggest that increased flow may be one of the mechanisms accounting for meridian system responses during acupuncture.