The synthesis of radioiodinated meta-iodobenzylguanidine (MIBG), a physiologic norepinephrine analog, was first accomplished by a group from the University of Michigan. Since the first report of the detection of pheochromocytoma with MIBG in humans, there have been several studies about the role of this agent in the diagnosis of pheochromocytoma and neuroblastoma. With a sensitivity of about 90% and a specificity of nearly 100% MIBG has been shown to be a reliable diagnostic tool for the detection and follow-up of pheochromocytoma.