Diets containing soybean protein generally induce low levels of serum cholesterol in experimental animals, when compared with diets containing casein. The hypocholesterolemia in animals fed soybean protein is associated with increased rates of fecal excretion of bile acids and neutral steroids, low liver cholesterol concentrations, increased numbers of hepatic apo B/E receptors, increased rates of hepatic cholesterol synthesis, increased rates of bile acid synthesis and decreased rates of lipoprotein cholesterol output by the liver. In this communication the development of the hypocholesterolemia induced by soybean protein is described. The various mechanisms that have been proposed to explain the hypocholesterolemic effect of soybean protein are scrutinized, compared and contrasted.