The dipping of snuff provoked paroxysmal hypertension that induced myocardial ischemia in a 69-year-old woman with pheochromocytoma. The diagnosis of her tumor was delayed by a report of a falsely low urine metanephrine level, resulting from interference with the metanephrine assay by meglumine present in the urine because of contrast coronary angiography performed on the day of urine collection. (JAMA 1984;252:2860-2862)