The dissociation constant (Kd = 1.8 ± 0.2 μM) for STxB in the model glycocalyx decreased by approximately three orders of magnitude compared to that previously reported for the highest-affinity individual STxB/Gb3 oligosaccharide interaction (Kd = 1.5 ± 0.5 mM). This is clear evidence for the enhanced binding due to multivalency effects in a system that differs from the presentation of Gb3 in lipid membranes. Comparison of ΓSTxB,max (3.1 ± 0.2 pmol/cm 2 ) with the total surface density of Gb3 oligosaccharides (37.6 ± 0.1 pmol/cm 2 , Table ) reveals a glycan:STxB pentamer ratio larger than 10. For CTB, these effects were even more pronounced, with the Kd decreasing by approximately 11,000fold (from 10 ± 3 mM for a single CTB/Le x binding site to 0.9 ± 0.1 µM in the model glycocalyx) and a minimal glycan:CTB pentamer ratio of approximately 30 (derived from ΓCTB,max = 1.3 ± 0.1 pmol/cm 2 and Γ Le x = 36.1 ± 0.2 pmol/cm 2 (Table )).