A new acetylated triterpene saponin was isolated from Herniaria glabra. GC, GC-MS, FAB-MS analysis and the use of 2D NMR techniques allowed the elucidation of its structure as 28-O-(beta-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)- [beta-D-glucopyranosyl-(1-->3)]-4-acetyl-beta-D-fucopyranosyl(1-->))- medicagenic acid-3-O-beta-D-glucuronide.