Monoamine oxidase is a complex enzyme system widely distributed in the body and is believed to be of primary importance in health and disease. Since the early work with iproniazid, a potent amine oxidase inhibitor, demonstrated that it stimulated the central nervous system, numerous related and unrelated compounds that inhibit this enzyme system have been investigated experimentally and clinically. Results have shown, however, that none of these drugs inhibits amine oxidase selectively. Hence it is unknown whether all clinical effects observed result from this or other pharmacologic actions. Pharmacologic Action The administration of monoamine oxidase inhibitors to experimental animals has been reported to result in increased amounts of serotonin, levarterenol, and related substances within the central nervous system.1 The excitability which appears in animals is thought by some investigators to simulate the antidepressant action of these compounds in human patients. The drugs have also been reported to produce a