Abstract Evidence is presented for the presence of a lectin on Streptococcus sanguis with specificity towards the major acidic oligosaccharide of human salivary mucin. Based upon hemagglutination inhibition studies, the strongest inhibitor was NeuAcα2,3Galβ1,3GalNAcol ⪢ NeuAcα2,3Galβ1,4Glc ⪢ NeuAc > Gal. Interactions were not heat sensitive or charge dependent, and were not affected by the presence of bacterial cell associated neuraminidase. The lectin could be extracted from Streptococcus sanguis with lithium 3,5-diiodosalicylate (LIS). Incubation of LIS extracts with carbohydrate ligands demonstrated that the specificity of binding was NeuAcα2,3Galβ1,3[ 3H-]GalNAcol ⪢ Galβ1,3[ 3H-]GalNAcol .