This lectin is a family of tetrameric glycoproteins consisting of combinations of A and B subunits similar in structure to PHA and GSL I. The dominant isolectins in our preparations appear to be B subunit-rich. VVL recognizes preferentially α- or β-linked terminal N-acetylgalactosamine, especially a single α-N-acetylgalactosamine residue linked to serine or threonine in a polypeptide (the Tn antigen). Evidence suggests that this lectin also may require specific amino acid sequences at the receptor site of glycosylation. The disaccharide galactosyl (α-1,3) N-acetylgalactosamine is also a potent inhibitor of this lectin.