The aerial part of Artemisia douglasiana Besser (6) has been used in folk medicine as a cytoprotective agent against the development of peptic ulcer. The dehydroleucodine (DhL), its active principle, significantly prevents the formation of gastric lesions induced by the exposure of the rats to absolute ethanol orally administered. The stomachs of control and experimental rats (after ethanol and pretreated with DhL) were removed, opened along the greater curvature and studied under stereo microscope and with light and scanning electron microscope. Absolute ethanol produced focal visible hemorrhagic lesions, extensive hyperemia, vascular stasis, cell disruption, and necrosis of the mucosa. Abundant mass of mucus was observed with scanning. The stomachs of rats pretreated with DhL showed a reduction of lesions. No hemorrhage and hyperemia were observed. The epithelia of the mucosa had a cobblestone appearance, similar to control rats and was covered by a fine layer of mucus. The mechanism of the protective action of DhL is unknown although it seems to be related to endogenous prostaglandins (PG).