Receptors for corticotropin-releasing factor (CRF) are members of a family of G protein-coupled receptors ("Family B") that respond to a variety of structurally dissimilar releasing factors, neuropeptides, and hormones (including secretin, growth hormone-releasing factor, calcitonin, parathyroid hormone, pituitary adenylate cyclase-activating polypeptide, and vasoactive intestinal polypeptide) and signal through the cyclic AMP and/or calcium pathways. To date, three genes encoding additional CRF-like peptides (urocortins) have been identified in mammals. The urocortins and CRF bind with differential ligand selectivity at the two mammalian CRF receptors. This report was prepared by the International Union of Pharmacology Subcommittee on CRF Receptors, to summarize the current state of CRF receptor biology and to propose changes in the classification and nomenclature of CRF ligands and receptors.