Measurement of catecholamines and their metabolites may be indicated when evaluating patients with hypertension, dizziness, syncope, or “spells” with some combination of headache, abdominal pain, sweating, tachycardia or palpitations, anxiety, pallor or flushing, and hypertension. Catecholamine metabolites are generally measured when pheochromocytoma or paraganglioma is suspected, although they can also be elevated in neuroblastoma. This chapter reviews different ways to measure these catecholamines and their metabolites, the sensitivity and specificity of each type of measurement, and medications and other compounds that may interfere with measurement.