Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel hypothalamic peptide structurally related to vasoactive intestinal peptide (VIP) and glucagon like peptide-1(7-36) amide (tGLP-1) in its N-terminal portion. Therefore, their levels of insulinotropic potency were compared using an isolated rat pancreas perfusion. It was found that 0.1 nM PACAP (1-27) amide (PACAP27) significantly stimulated insulin release under a perfusate glucose concentration of 5.5 mM, whereas 1 nM PACAP27 did not under a perfusate glucose concentration of 2.8 mM. The potency was evaluated as tGLP-1 greater than PACAP27 greater than VIP. These results indicate that PACAP is a glucagon superfamily peptide which stimulates insulin release in a glucose dependent manner.