Orphanin FQ (OFQ, Nociceptin) is a recently discovered 17-amino acid neuropeptide that is structurally related to the opioid peptides but does not bind opioid receptors. OFQ selectively binds its own receptor (OFQR), which is also sequentially related to the opioid receptors, yet does not bind opioid ligands. OFQ has been proposed to act as an anti-opioid peptide, but its widespread sites of action in the brain suggest that it may have more general functions. Nociceptin acts as an anxiolytic to attenuate behavioral responses to stress. In vivo experiments have demonstrated that Nociceptin modulates a variety of biological functions ranging from nociception to food intake, from memory processes to cardiovascular and renal functions, from spontaneous locomotor activity to gastrointestinal motility, from anxiety to the control of neurotransmitter release at peripheral and central sites. Nociceptin has being shown to directly inhibit an adaptive immune response, i.e., antibody formation, both in vitro and in vivo.