The main function of the peptide hormone gastrin is to stimulate the parietal cells of the stomach to produce hydrochoric acid. Produced in the stomach and duodenum, gastrin enters the circulation, and returns to the stomach to produce most of its effects. These effects include binding to cholecystokinin2 receptors to cause histamine release, causing the release of the digestive proenzyme pepsinogen, and stimulating growth and maturation of cells in the gastric mucosa. Gastrin is synthesized as a preprohormone, and then processed from the amino-terminus to several forms. We offer the human 17-amino acid peptide with and without sulfation of tyrosine12. Both forms are active. Unsulfated rat gastrin has a slightly different amino acid composition and is useful for animal research. We also offer a synthetic unsulfated human gastrin in which methionine15 is replaced with leucine for increased stability in aqueous solution.