Because of the large amount of material that has been published since the last review of Terpenes, Saponins, and Closely Related Substances (1) , the present review has been limited to the triter penes. Even for this group of compounds, all of the detailed chemistry on which the arguments for structure are based will not be given but only a summary of the present status of the fleld.1 Besides those ap pearing previously in this publication (l, 2, 3), mention should be made of the excellent reviews of this field by Haworth (4) and by Spring (5). The triterpcnes are natural products containing thirty carbon atoms whose carbon skeleton is believed to be divisible into isopentanp units (isoprene rule) . They are distributed widely in the plant king dom and maY' occur in alI parts of the plant, free or combined with sugars. The glycosides constitute one group of the saponins and the aglycones formed on hydrolysis usually are referred to as triterpene sapogenins.2 Table I lists the sources and molecular formulas of the more extensively investigated triterpenes, while Table II lists some compounds which probably are triterpenes and have been the subject of recent investigations. It is of interest to note that whereas previ ously all triterpenes, with the exception of the open-chain hydrocarbon squalene, have been obtained from plant sources, lanosterol and agnos terol were isolated first from wool fat where they are associated with the zoosterol, cholesterol (21) . Both lanosterol and cryptosterol are present in the complex mixture of phytosterols from yeast (20) and �-amyrin is associated with the phytosterols, stigmasterol and sitos terol, in the dandelion root (50) . Zimmermann (37) has stated that whereas triterpenes have been isolated from all parts of different plants, only in the case of the dande lion have triterpenes been shown to be present in different parts of the same plant. It seems probable that other cases will be found but in