Ricin (RT) is a potent toxin found in the castor bean plant, Ricinus communis. Due to its toxicity and the ease of obtaining and disseminating, RT is classified as a category B biological warfare agent by the Centers for Disease Control. The ricin A chain (RTA) is an N-glycosidase which catalyzes cleavage of adenine A₄₃₂₄ from rRNA, thereby halting protein production by the cell. The ricin B chain (RTB) is a lectin with two binding sites specific for glycosphingolipids (GSLs) and glycoproteins containing terminal galactose residues. The purpose of this research was to synthesize and characterize effective ligands for RTB, and to study their effects on ricin binding and localization within mammailian cells. Because multivalent carbohydrates are generally better ligands for lectins than monovalent ones, we hypothesized that RTB, with its two binding sites, would bind preferentially to multivalent carbohydrate ligands. Comparison of IC₅₀'s obtained for RTB binding to bovine serum albumin (BSA) derivatized with an average of 32 lactosyl residues (IC₅₀=11.5nM) indicated that it was a more effective inhibitor than monovalent lactose (IC₅₀>10,000nM). To further understand these observations, surface plasmon resonance was used to determine the binding affinity of RT and RTB to some of the inhibitors. The results indicated that RT and RTB had similar affinities for each ligand tested. Interestingly, studies with just RTB indicated that it exhibited different binding affinities when the ligand was immobilized on a carboxy methyl dextran surface compared to when it was in solution. Results of the inhibition studies with RTB, support the conclusion that it adheres to multivalent carbohydrate substrates more efficiently than to monovalent ones. Data from binding studies may be useful in identifying which steps involved in ricin intoxication might be viable targets for development of compounds that could be used as anti-toxins in the event of RT exposure.