A series of sesquiterpene compounds possessing both eudesmane and eremophilane skeletons were tested as gastric cytoprotective agents on male Wistar rats. The presence of an alpha,beta-unsaturated aldehyde on the C-7 side chain together with a hydroxyl group at C-4 is the requirement for the observed antiulcerogenic activity. In an attempt to establish new molecular structural requirements for this gastric cytoprotective activity, a structure-activity study was performed.