Human colorectal, pulmonary carcinoma as well as neuroblastoma have been shown to be rich in opiate receptors. A possible targeted fusion protein,consisting of Enkephalin and αⅠ interferon, was constructed, bacterially expressed, and purified. When injected intracerebrally into mice, enkephalin-αⅠ interferon fusion protein caused more potent analgesia than αⅠ interferon. The analgesia effects of the fusion protein were prevented and reversible by opiate antagonist, naloxone and naltridole. The fusion protein also inhibits bindings of ［³H］ DPDPE to opiate receptor. The enkephalin-αⅠ interferon fusion protein was shown to have more antiproliferative and antitumor activities against opiate receptor-bearing tumors, both in vivo and in vitro.These results suggest enkephalin-αⅠ interferon fusion protein may be able to target opiate receptors on tumor cells.