IN recent years neuraminic acid1 and several of its derivatives, such as sialic acid and lactaminic acid, have been shown to be constituents of mucoproteins, gangliosides and related naturally occurring substances. Although the chemical structure of neuraminic acid has not been established as yet, its elementary composition and some of its chemical properties are known. The existence of this substance as either the free carboxylic acid or its corresponding lactone form has been demonstrated2, and it has been postulated that a hexosamine residue is present3. The biological function of neuraminic acid remains obscure, although recent evidence indicates that this compound is liberated from its parent polysaccharide by the action of influenza virus or virus-receptor-destroying enzymes3,4.