The stems of Marsdenia tomentosa contain a glycoside mixture. The alkaline hydrolysate of the crude aglycones showed the presence of sarcostin and two new aglycones. The structures of those two new materials, tomentogenin and dehydrotomentogenin has been proved. Tomentogenin was shown to be identical with 5α-dihydroutendin and dehydrotomentogenin with utendin. The structures of these latter materials were determined about the same time as this work by Reichstein.