Gastric ulcers induced in dogs by transserosal injection of 1 ml of 40% acetic acid healed completely by the 7th week after ulceration and never reulcerated during the observation period up to 12 weeks. Acetic acid ulcers in the active (at 1 week), quiescent (3 weeks) or healed (at 7 weeks) stages were not influenced by the daily administration of aspirin 2 g/dog/day for 5 consecutive weeks. All examinations were done by gastroscopy in addition to macroscopical and histological observations at autopsy.