Inhibition of monoamine oxidase by metaiodobenzylguanidine, a new radiodiagnostic agent.

Metaiodobenzylguanidine, which is used in the diagnosis and treatment of pheochromocytoma, produced 50% inhibition of monoamine oxidase at a concentration of 8 X 10(-6) M in vitro. These results suggest that a careful study of the structure of a new radiodiagnostic agent should be done to anticipate and prepare for possible unwanted biological effects when administering the preparation to patients.