(vă-nil'il-man-del'ik as'id), Misnomer for 4-hydroxy-3-methoxymandelic acid (α,3-dihydroxy-2-methoxybenzeneacetic acid); the major urinary metabolite of adrenal and sympathetic catecholamines (for example, from both epinephrine and norepinephrine); elevated in most patients with pheochromocytoma.