Dust discharged into the air during soybean unloading from ships has caused asthma epidemics in Barcelona, Spain. The possibility was considered that the allergen developed during the sea voyage from Toledo, Ohio or San Paulo, Brazil, where the beans were loaded. Soybean plants were collected from a field near Rochester, Minnesota at various stages of growth and tested for the presence of allergen. Leaves, stems, and flowers of immature soybean plants contained small amounts of allergen, while immature soybean telae contained large amounts of the allergen. Large amounts of allergen were found in telae from ripe beans picked before the pod opened. Preliminary studies of extract dusts from corn, oats, wheat and barley suggested that a cross reacting allergen was present. Sera from three residents of Barcelona were used to identify and quantify soybean allergens in soybean plant parts, dusts from grain storage areas, a soybean hull (tela) extract and a low molecular weight fraction of the hull extract. The low molecular mass (MM) allergen fraction was found in small amounts in all parts of the plant and at every stage of development. At least part of the corn and oat allergens exist in an MM range similar to the soybean allergen, although in the latter source they are found in much greater quantities.