During the last decade, a new group of drugs, known as the barbiturates, has come into prominence in veterinary medicine as hypnotics and anesthetics. Today we find that these derivatives of barbituric acid are used quite extensively in human medicine and in the small animal field of veterinary medicine. The therapeutic action of the derivatives of this parent barbituric acid molecule, which is weakly acid but has no sedative or hypnotic effect, has been made possible because one or both of the hydrogens on the side chains are replaceable. Thus, barbital or diethyl barbituric acid was obtained by replacing each hydrogen with an ethyl radical, forming a derivative which did possess hypnotic and sedative action.