We used NMR spectroscopy, molecular modeling and infectivity competition assays to investigate the key interactions between the spike protein (VP8*) from 'sialidase-insensitive' human Wa and 'sialidase-sensitive' porcine CRW-8 rotaviruses and the glycans of gangliosides GM1 and GD1a. Our data provide strong evidence that N-acetylneuraminic acid is a key determinant for binding of these rotaviruses. This is in contrast to the widely accepted paradigm that sialic acids are irrelevant in host cell recognition by sialidase-insensitive rotaviruses.