Cismonoenoic acids form readily from unsaturated fatty acids in animal tissues, with palmitoleic acid (9-cis-hexadecenoicacid) deriving from palmitic acid. An intermediate, 1Δ2-trans-hexadecenoicacid, arises during the β-oxidation of palmitic acid. Furthermore, Δ2-trans-hexadecenoicacid, at a dose of 10 mg/kg, significantly reduces gastric juice secretion in pylorus-ligated rats, indicating potential for gastric ulceration simulation models.