A method is provided for detecting the presence of C. difficile toxin A. Stool or other appropriate specimen is contacted with a reagent containing an available non-reducing galactose-alpha-1-3-galactosyl structure, which is a specific receptor for toxin A. The reagent may be intact cells, cell membranes, membrane fractions containing the toxin A receptor structure, glycoconjugates, as well as the purified toxin A receptor 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 is used to detect, isolate, or purify biological materials of interest containing the receptor structure.