A number of polypeptidic hormones, mainly expressed in the intestine or the pancreas, belong to a group of structurally related peptides [1,2]. Members of this family are:

• Glucagon, which promotes hydrolysis of glycogen and lipids, and raises the blood sugar level.
• Glucagon-like peptide 1 (GLP-1), a peptide of unknown function processed from the same precursor protein as that of glucagon.
• Glucagon-like peptide 2 (GLP-2), a peptide of unknown function also processed from the glucagon precursor protein but which, in contrast to GLP-1, is only found in mammals.
• Gastric inhibitory polypeptide (GIP), which is a potent stimulator of insulin secretion and a relatively poor inhibitor of gastric acid secretion.
• Secretin, which stimulates formation of NaHCO(3)-rich pancreatic juice and secretion of NaHCO(3)-rich bile as well as inhibiting HCl production by the stomach.
• Vasoactive intestinal peptide (VIP), which causes vasodilatation, lowers arterial blood pressure, stimulates myocardial contractility, increases glycogenolysis and relaxes some smooth muscles.
• Peptide PHI-27, a vasodilator peptide which is coded by the same precursor protein as that of VIP.
• Growth hormone-releasing factor (GRF) (also known as somatoliberin), which is released by the hypothalamus and acts on the adenohypophyse to stimulate the secretion of growth hormone.
• Pituitary adenylate cyclase activating polypeptide (PACAP) [3].
• Helospectin (exendin-1), helodermin (exendin-2), exendin-3, and exendin-4 from the venom of gila monsters. The exendins are peptides with a VIP/ secretin biological activity [4].
• A peptide produced by the X-cells of the islets of ratfish pancreas [5].

As a pattern for this family of peptides (which are from 30 to 45 amino acid residues long), we used the more or less conserved first ten positions of the N-terminal as well as a conserved hydrophobic residue in position 23.