IT would appear that the chemical relationship of the substances designated by various names such as neuraminic, sialic, lactiminic and gynaminic acid has been established. In order to avoid further confusion we propose to call the basic, unsubstituted compound neuraminic acid. Sialic acid is suggested as group name for the acylated neuraminic acids (for example, N-acetylneuraminic acid, N-glycolylneuraminic acid, diacetylneuraminic acids). For the enzyme which splits the glycosidic linkage joining the terminal sialic acid to the residual oligo- or polysaccharide the names neuraminidase and sialidase may be used synonymously. We have agreed to use this nomenclature in future.