Trefoil peptides are protease resistant molecules secreted throughout the gut that play a role in mucosal healing and protection of the gastrointestinal epithelia. These peptides contain three intrachain disulfide bonds, forming the trefoil motif, or P-domain. SP (spasmolytic polypeptide), also designated Trefoil factor 2 (TFF2) precursor, is a trefoil protein that functions to inhibit gastrointestinal motility and gastric acid secretion. SP may also act as a structural component of the gastric mucus, possibly by stabilizing glycoproteins in the mucus gel through interactions with carbohydrate side chains. A downregulation of SP expression is associated with primary gastric cancer, and a progressive loss of this protein is likely to be involved in the early stage of the multi-step gastric carcinogenesis pathway.