Collect 24 hour urine specimen. Add 25 mL of 50% glacial acetic acid (15 mL for pediatric patients) to container prior to start of collection. Following collection, mix well, measure 24 hour urine volume, aliquot 20 mL into a plastic urine container and refrigerate. Record total 24 hour urine volume and collection dates/times on request form. Specimens with no preservative are also acceptable: add 50% glacial acetic acid to container following collection, mix well and send 20 mL aliquot (preferred); alternatively a non-acidified aliquot will be accepted. Patient must be off Aldomet (alpha methyldopa) and its derivatives for a period of not less than 5 weeks. This drug will falsely elevate the metanephrines and normetanephrines. A 12 hr overnight collection will be accepted, but reference ranges have been established only for 24 hr collections.