The undigested high-molecular weight fraction (HMF) of soybean protein prepared after exhaustive digestion either by microbial proteases or by pepsin exerted a remarkable hypocholesterolemic activity compared to the parent protein in rats fed cholesterol-enriched diets. HMF bound in vitro with bile salts and stimulated fecal excretion of both neutral and acidic steroids far more than did soybean protein. Extraction of HMF with methanol slightly decreased the activity, but the methanol soluble fraction was not regarded as a principle determinant. Further degradation of the methanol-extracted HMF by various proteases resulted in loss of activity. Bile acid binding capacity of HMF from other vegetable proteins was lower than that from soybean protein.