Different compounds, including drugs ulcerogenic for man (acetylsalicylic acid, phenylbutazone, indomethacin, and reserpine), drugs not producing ulcers in man (aminopyrine, desoxycorticosterone, chlorpromazine, diphenydramine, methantheline, and vitamin C) or not well known under this respect (cortisone, prednisone), and drugs never investigated (tetracaine and procaine) have been studied in rats and compared with benzydamine, a new analygesic antiinflammatory compound. In the basic experiment, consisting of a single administration to rats thereafter fasted for 6 or 24 hours before examination of the stomach, only the first class of compounds was clearly ulcerogenic for rats. When given to rats fasted for 24 hours, some compounds not ulcerogenic for man (chlorpromazine, diphenydramine, methantheline) and prednisone, and tetracaine, also produced ulcers. Reserpine, chlorpromazine, and to a lesser extent, cortisone and prednisone, produced gastric ulcerations when given daily for 1 week. The corticoids produced a significant degree of ulceration when given for a week to rats fasted every other day. In experiments carried out in rats fasted for 4 days unconclusive results were obtained, because of the high percentage of gastric lesions and deaths in control animals. In experiments on restraint ulcers only reserpine produced gastric lesions in much lower doses than in normal rats, while chlorpromazine exerted a protective action. Benzydamine did not produce any ulcerogenic action in any of the experimental conditions used. Significance of these results is discussed.