Recent reports provided evidence that at least two δ opioid receptors may mediate antinociception in mice. In this study, we studied further the involvement of δ opioid receptor subtypes in mediating antinociception at spinal sites in mice using subtype selective agonists and antagonists. The antinociceptive ED50 values (95 % C.I.) of i.t. administered DPDPE [(D-Pen2, D-Pen5)enkephalin] (δ1 receptor agonist) and DELT II [(D-Ala2)deltorphin II] (δ2 receptor agonist) were 6.3 (5.2-7.6) and 6.4 (5.4-7.7) nmol/mouse, respectively. Administration of BNTX, s.c. increased the antinociceptive ED50 value of DPDPE 5.9-fold whereas that of DELT II was not changed significantly. On the other hand administration of maltriben (NTB, the benzofuran derivative of naltrindole), s.c. increased the antinociceptive ED50 value of DELT II 12.5-fold but did not alter that of DPDPE. Similarly administration of BNTX, i.t. increased the antinociceptive ED50 value of DPDPE 4-fold without altering significantly that of DELT II. NTB given i.t. enlarged the antinociceptive ED50 of DELT II 11-fold without affecting significantly that of DPDPE. BNTX, s.c. did not alter the antinociceptive ED50 values of the μ-agonists, DAMGO [(D-Ala2, MePhe4, Gly-ol5) enkephalin] and morphine or that of the κ-agonist, U50,488H [trans(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinylcyclohexyl]benzeneacetamide] These results demonstrate that BNTX is highly selective for δ1 opioid receptors at spinal sites. Also, the present data provide for the involvement of both δ1 and δ2 opioid receptors in mediating antinociception at spinal sites in mice.