A 29-yr-old white woman was hospitalized with bloody diarrhea secondary to ulcerative colitis. Within 24 h of receiving intravenous steroids, loperamide, and mesalamine, she developed symptomatic hypotension, severe sinus bradycardia, sinus pauses, and junctional escape beats. The hypotension and sinus bradycardia resolved after discontinuing mesalamine. She had a family history of conduction tissue disease but her exercise ECG and Holter studies were normal. She was rehospitalized 6 wk later with an exacerbation of ulcerative colitis and, within 8 h of receiving mesalamine, developed hypotension and severe sinus bradycardia, which resolved after stopping mesalamine. Thus mesalamine should be used with caution, especially in patients predisposed to cardiac conduction tissue disease.