A method is provided for detecting the presence of C. difficile toxin A. Stool or other appropriate specimen is contacted with a reagent containing the human X, Y or I-antigens, each of which is a specific receptor for toxin A. The reagent may be intact cells, cell membranes, membrane fractions containing any of these antigens, glycoconjugates, as well as the purified oligosaccharide antigen per se. Binding of toxin A is determined by conventional assay techniques. The method may also be used to isolate and purify toxin A. Conversely, immobilized toxin A may be used to detect, isolate, or purify biological materials of interest expressing the X, Y or I antigens.