In the food, particularly the feed, industry, large quantities of soya bean protein products are used for the formulation of end-products destined for human or animal consumption. These basic ingredients and the final end products often have to fulfill specific requirements regarding the presence of antinutritional compounds (ANCs) and their allergenic potential. Therefore, a special need exists for the identification and characterization of ANCs and the causative factors behind allergy and hypersensitivity. This paper describes the results of a comparative study of a previously identified unknown antigenic soya bean P22-25 protein with the first, recently described Gly m I (or P34) soya bean allergen. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and Western blotting analysis were carried out using calf anti-soya protein sera and a marine anti-Gly m I (or P34) monoclonal antibody in order to detect the antigenic soya bean P22-25 protein and the allergen Gly m (or P34) respectively. The results showed that these proteins were different. In addition, a number of industrial soya bean products were analyzed for the presence of both apparent antigenicity (essentially β-conglycinin and P22-25) using calf anti-soya protein sera and the allergen Gly m I (or P34), and both β-conglycinin, P22-25 and P34 could be detected to a varying extent in the products analyzed.