Much was known of the pharmacology of meta-iodobenzylguanidine (MIBG) before its clinical use, but we have since learned a good deal more about the metabolic distribution and fate of this radiopharmaceutical. And, as is the nature of science, more is yet to be discovered. This communication reviews what is known about the pharmacology of radiolabeled MIBG and how this pharmacology affects the clinical studies that use the agent.