9-Hydroxy-19,20-bis-nor-prostanoic acid (IBI-C83) was evaluated on gastric acid secretion and gastric lesions induced in laboratory animals by a variety of experimental conditions: compound IBI-C83 is proved effective in decreasing basal, histamine- and pentagastrin-stimulated total acid output in rats and in pentagastrin perfused dogs. The concentration of N-acetylneuraminic acid in the gastric fluid, a marker of mucus secretion, is enhanced in rats by IBI-C83. This drug prevents gastric damage induced by non-steroidal antiinflammatory compounds such as acetylsalicylic acid, indometacin and phenylbutazone, gastric ulcers following pylorus ligation, and facilitates healing of the gastric ulcers evoked by subserosal injection of acetic acid. A prominent feature of IBI-C83 is its capacity to protect the rat from gastric damage elicited by necrotizing agents such as absolute ethanol, hydrochloric acid and hypertonic saline. This property, called "cytoprotection" and common to naturally occuring prostaglandins, is independent on the antisecretory activity of IBI-C83 and is not shared, at least in the reported experimental models, by the H2-receptor antagonist cimetidine. In spite of the prostaglandin-like properties displayed in its cytoprotective activity, compound IBI-C83 does not affect cardiovascular functions, gastrointestinal transit and uterine motility.