The use of saponin in experimental vaccines has been known for more than 60 yr (1, Chapter 9) and generally it is more active as an adjuvant with strongly immunogenic antigens. A number of saponins are derived from the bark of the South American soaptree (Quillaja saponaria) as acylated triterpenoids each having quillaic acid as the aglycone but with different glycosidic side chains. From the crude preparations it has been possible to refine purer mixtures, e.g., Quil A (2) and QS-21 (3). These have been shown to exert an adjuvant effect at doses as low as 5.0–20.0 μg. Because a wide variety of foods contain saponins there is potential for their use in oral vaccines, but there has been some reluctance to use them parenterally because of their known membranolytic and hemolytic effects; ISCOMs have not been shown to possess hemolytm activity at the usual dose levels used in animals.