Pharmacological effects of a novel opioid receptor-like1 (ORL(1)) receptor antagonist, [N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl) benzamide monohydrochloride] (JTC-801), were examined in in vitro and in vivo. JTC-801 inhibited the binding of [(3)H]-nociceptin to human ORL(1) receptors expressed in HeLa cells with a K(i) value of 44.5 nM. JTC-801 completely antagonized the suppression of nociceptin on forskolin-induced accumulation of cyclic AMP (IC(50) : 2.58 microM) using ORL(1) receptor expressing HeLa cells in vitro. In in vivo, when given intravenously at dosages of 0.01 mg kg(-1) and above, or orally at dosages 1 mg kg(-1) and above, JTC-801 antagonized the nociceptin-induced allodynia in mice. Effects of JTC-801 on various nociceptive models were examined. In mouse hot-plate test, JTC-801 prolonged escape response latency (ERL) to exposed heat stimulus with minimum effective doses (MED) of 0.01 mg kg(-1) by i.v. or 1 mg kg(-1) by p.o. In the rat formalin test, JTC-801 reduced both the first and second phases of the nociceptive response with MED of 0.01 mg kg(-1) by i.v. administration or 1 mg kg(-1) by p.o. administration. This anti-nociceptive action of JTC-801 was not inhibited by naloxone (10 mg kg(-1), s.c.). We have demonstrated that JTC-801 antagonizes the ORL(1) receptor response, and that JTC-801 has efficacious and potent anti-nociceptive effects in acute pain animal models not only by intravenous injection but also oral administration. These results suggest that JTC-801 may represent a new class of analgesics.