RESUMO
Pheochromocytomas and/or paragangliomas are rare, heterogeneous tumors of the chromaffin cells. Thirty percent of the patients presented with these diseases in a hereditary context. The biological diagnosis relies on the identification of excessive secretion of the metanephrines which are more sensitive and specific than those of catecholamines. The published recommendations give the opportunity to choose between the metanephrines in sera or urines. The concentrations of the free plasmatic metanephrines reflect the ongoing production of tumor. They are little sensitive to the renal failure. The gold standard method to measure the free metaphrines in plasma is the LC-MS/MS chromatography. This is the technical event that we use since 2008, and we relate our experience.