Kayexalate (Roxane Labs, Columbus, OH) in sorbitol is commonly administered by the oral and rectal route for the treatment of hyperkalemia in patients with renal failure. It is believed to have minimal toxicity because it functions as a cation exchanger and is not absorbed. We herein report on a patient who developed identical serpiginous ulcers in the stomach and the terminal ileum after the use of Kayexalate. We believe that this drug could have significant gastrointestinal toxicity in specific patient groups and suggest tentative guidelines, both for the identification of such patients and for the safer use of Kayexalate in these circumstances.