The hemolytic properties and the adsorbability on red blood cells of saikosaponin a, saikosaponin d and 13 metabolites formed in the alimentary tract were investigated. Among these compounds, saikosaponin d and its intestinal product, prosaikogenin G, which possess an α-hydroxyl function at C16, showed the strongest hemolytic activity at the dose range of 1.0 to 5.0 μg/ml. Saikosaponin a and its intestinal product, prosaikogenin F, which possess a β-hydroxyl function at C16, showed activity above 10 μg/ml. In this case, the monoglycoside, prosaikogenin F, showed the stronger activity than the diglycoside, saikosaponin a. Among the gastric products whose ether ring was cleaved to produce a carbinol, the monoglycosides, prosaikogenin A and prosaikogenin H, showed a slight activity above 25 μg/ml, and the saikogenins except saikogenin A were inactive. Saikogenin A, however, had hemolytic activity at a dose of 15 μg/ml. The adsorbabilities of these compounds on red blood cell membranes closely paralleled their degrees of hemolytic activity.