Rare cases of hepatotoxicity have been attributed to the antiarrhythmic agent procainamide. We here describe the case of a patient who had a hypersensitivity reaction to procainamide with fever, chills, arthralgia, abdominal pain and acute elevations of serum aminotransferase activities and bilirubin concentration. The reaction occurred after the patient had received a large intravenous dose during cardiac electrophysiological testing. This case should alert physicians to potential hepatotoxic reactions to procainamide, particularly with the increasing popularity of cardiac electrophysiological testing, during which this drug is commonly used.