Gastric ulcers were produced in rats by forced muscular exercise (“exertion ulcers”). These ulcers were multiple, bleeding, located in the corpus, consisted of hemorrhagic necrosis of the mucosa, and could easily be counted. The animals were fasted overnight prior to exertion. Female rats were more sensitive than males to this type of ulcer. Agents known to reduce gastric acidity (anti-cholinergics, antacids, mercuric acetate) prevented their formation, as did prednisolone. Neither adrenalectomy nor administration of desoxycorticosterone affected these ulcers. During exertion, volume and acidity of gastric juice were reduced. Although the pathogenesis of these ulcers remains to be elucidated, the following chain of events is offered as a hypothesis: Exertion (severe stress) → vascular shock → impairment of gastric circulation → gastric anoxia → decreased resistance to autodigestion → ulcers.