Corticotropin-releasing factor (CRF), a peptide isolated from ovine hypothalamus, and sauvagine, a peptide isolated from frog skin, share significant structural homology and elicit a number of similar biological responses. CRF is more potent than sauvagine in stimulating pituitary ACTH secretion. Sauvagine, however, is 5-10 times more potent than CRF to act within the brain to increase plasma levels of catecholamines and glucose and to elevate mean arterial pressure. Sauvagine is likewise more potent than CRF to act outside the brain to increase superior mesenteric artery flow and plasma glucose concentrations and to decrease mean arterial pressure. CRF and sauvagine produce important effects representative of biologically active peptides.