Recent evidence has indicated that vasopressin (VP) can increase the pain threshold. It is not clear whether the paraventricular nucleus (PVN) of hypothalamus, which is one of the main nuclei that secrete VP in brain, is involved in the acupuncture analgesia (AA). The present study was designed to examine the role of PVN in AA. Experiments were carried out on Wistar rats using tail stimulation vocalization test to measure the pain threshold. The acupoints "Renzhong" and "Chengjiang" were selected for electroacupuncture. Electrical stimulation of PVN could increase significantly the pain threshold and enhance the effect of AA. On the contrary, electrolytical lesion of PVN could decrease the effect of AA obviously, which could be recovered by cerebroventricular injection (ICV) of 300 ng of arginine VP. Pretreatment with AVP-antiserum (ICV) could attenuate the effect of AA. These data indicated that PVN plays an important role in pain modulation and in the effect of AA. This role might be mediated by the VP-containing neurons in PVN.