This article presents an experimental method using cats for investigation of the local ulcerogenic properties of oral drugs in the esophagus. 15 drugs in current clinical use were tested. The drugs were placed in esophagus and the animals were sacrificed after 5--8 h, 4--7 or 21 days. The esophagus was cut open, photographed macroscopically and sectioned for light microscopy. Several drugs, e.g. doxycycline, alprenolol, propranolol, ferrosuccinate, ferrosulfate, and emepronium bromide showed marked ulcerogenic properties, whereas indomethacin and betamethasone did not cause any lesions in the cat esophagus. The results seem to be in accordance with the local effect these same drugs exert on the human esophageal mucosa. In order to predict and prevent drug-induced esophageal lesions in man we suggest that oral drugs should be tested concerning their local ulcerogenic properties in the esophagus.