Although central nervous system (CNS) depressant activity is ordinarily associated with compounds which may be classed as cyclic amides (barbiturates, hydantoins, oxazolidinediones), stimulant and convulsant activity have been found in a number of compounds of this class. 2-Imino-5-phenyl-4-oxazolidinone has recently been introduced into therapy as a CNS stimulant.