The type B-specific lectin from the mushroom Marasmius oreades was immobilized onto Sepharose 4B. The immobilized lectin bound murine laminin and bovine thyroglobulin, glycoproteins that contain the Galα1,3Galβ1,4GlcNAc epitope. This epitope is responsible for hyperacute rejection of xenotransplants from lower mammals to humans, Old World monkeys, or apes. The immobilized lectin also bound a fraction of serum proteins from type B human serum but little or none from type A or O(H) serum. The major protein bound from human B serum was a portion of the ≤2-macroglobulin. Treatment of this fraction with N-glycosidase F resulted in decreased molecular weight of bands associated with α2-macroglobulin and loss of their M. oreades lectin reactivity, whereas on treatment with coffee bean α-galactosidase, this bound fraction also lost reactivity with M. oreades lectin but became reactive with Ulex europaeus I lectin, suggesting the presence of L-fucosyl-α1,2-terminated structures. The presence of blood group epitopes on α2-macroglobulin has been detected previously by immunological methods, but this is the first isolation and characterization of the specifically glycosylated fraction of this serum protein. The immobilized lectin also bound a number of proteins from pig, rabbit, and rat serum that were distinct in electrophoretic mobility from the human B-serum components and presumably contain the xenotransplantation epitope among their glycan structures. This report further demonstrates the utility of immobilized lectins in isolating and characterizing glycan structures of naturally occurring glycoproteins.