Effect of the supernatant from cultural rat hippocampus cells (HCS), hippocam-pal extract (HE) and injection of panax quinquefoium soponin (PNS) into the hippocampus on immunopotent cells was studied. The results showed that proliferation of thymocytes could be promoted by HCS, and proliferation of the lymphocytes could be enhanced by injection of PNS into the hippocampus.These results suggest that the hippocampus may be involved in immunoregulation.