Binding between a component of the crude hot water extract obtained from Allium sativum crushed bulbs (ASw) and cholera toxin B pentamer (CTB) was detected by STD NMR experiments. Bioassay-oriented fractionation allowed the partial identification of a high molecular weight polysaccharide mainly composed of galactose as the bioactive complex against CTB. This work represents the first example of screening of a medicinal plant by NMR against a specific disease, and corroborates traditional medical uses of the species. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.