The IgE-binding proteins in soybeans were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the fractionated soybean proteins probed with the sera of the patients with atopic dermatitis. About 20% of the patients examined were shown to have specific IgE antibodies to soybean proteins. At least 16 soybean proteins with molecular weights ranging from about 70, 000 to 14, 000 were recognized by the sera of the patients: 10 major IgE-binding components were found in the 7S-globulin fraction, and the others mainly in the 2S-globulin and whey fractions. The IgE antibodies of the patients bound most strongly and frequently to a unique protein with molecular weight of about 30, 000 in the 7S-globulin fraction, which appeared to be the major allergen in soybeans and was named as Gly m Bd 30 K. The proteins in the 11S-globulin fraction were scarcely recognized by the patients' sera and assumed to be less allergenic for the patients with atopic dermatitis.