Affinity purified Vicia villosa lectin or agglutinin (VVL/VVA) is a tetramer composed of four subunits. VVL consists of A and B subunits, with a dominant isolectin that appears to be B subunit-rich. A4 isolectin agglutinates specifically A1 erythrocytes. B4 isolectin does not agglutinate A, B, or O-erythrocytes; however, B4 binds the Tn antigen, a molecule expressed on the surface of most tumor cells. A2B2 and similar tetramer isolectins display properties characteristic of both A4 and B4 isolections.Colloidal gold can be used to visualize localization of specific saccharide moieties and examine the distribution of plasma membrane glycoproteins based on the binding pattern of Vicia villosa Lectin (VVL/VVA). Colloidal gold labeled lectins can be viewed via electron microscopy.