A 17-year-old male who had been diagnosed with ulcerative colitis was prescribed 80 mg prednisolone and 1, 500 nig 5-aminosalicylic acid (5-ASA) per day. Two weeks after initiating therapy, he was referred to our hospital for evaluation of chest pain and high fever. Electrocardiography (ECG) showed ST elevation in limb and precordial leads. Chest pain with high fever and ECG changes were resolved after 5-ASA was discontinued. Three weeks later, the administration of a low dose of 5-ASA was associated with the immediate recurrence of pericarditis associated with chest pain, suggesting a hypersensitive reaction to 5-ASA in this patient.(Internal Medicine 40: 901-904, 2001)