There are two major classes of Neuraminidase that cleave exo or endo poly-sialic acids:
* Exo hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)-glycosidic linkages of terminal sialic acid residues
* Endo hydrolysis of (2→8)-α-sialosyl linkages in oligo- or poly(sialic) acids (see  endo-α-sialidase.)