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. Fluorescein labeled Vicia villosa lectin has an appropriate number of fluorochromes bound to provide the optimum staining characteristics for this lectin. This conjugate is supplied essentially free of unconjugated fluorochromes. The excitation maximum is at 495 nm and the emission maximum is at 515 nm.