A nondigitalized patient without heart disease, but with ulcerative colitis on parenteral hyperalimentation, developed ventricular tachycardia in association with hypomagnesemia. Magnesium infusions were successful in suppressing the arrhythmia, but because of ongoing fecal losses, hypomagnesemia and ventricular tachycardia recurred each time the infusion was stopped. After total colectomy, the patient remained normomagnesemic and free of arrhythmias. The few previous descriptions of arrhythmias attributed to hypomagnesemia in nondigitalized patients are reviewed. The importance of recognizing hypomagnesemia as an easily reversible cause of arrhythmias is stressed.