We discovered a potent nociceptin/orphanin FQ receptor (ORL1) receptor antagonist, J-113397 (1-[(3R, 4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1, 3-dihydro-2H-benzimidazol-2-one). J-113397 inhibited [125I][Tyr(14)]nociceptin binding to Chinese hamster ovary (CHO) cells expressing ORL1 receptor in a dose-dependent manner (IC(50); 2. 3 nM), but showed 600-fold or less affinity for mu-, delta- and kappa-opioid receptors. Nociceptin/orphanin FQ-induced suppression of cyclic AMP accumulation elicited by forskolin was completely inhibited by J-113397 with an IC(50) value of 26 nM. These results indicate that J-113397 is a potent and selective nonpeptidyl antagonist of the ORL1 receptor.