Further studies by means of preparative HPLC led to the isolation of two new furostanol saponins, macrostemonosides G (1) and I (3), along with an artifact, macrostemonoside H (2) from the bulbs of Allium macrostemon Bunge. On the basis of chemical evidence and spectral analyses (1H-,13C-NMR,1H-1H COSY,1H-13C COSY, HMBC and FAB-MS), the structure of 1 was established as 26-O-beta-D-glucopyranosyl-22-hydroxy-5 beta-furost-25(27)-ene-3 beta,12 beta,26 triol 3-O-beta-D-glucopyranosyl(1-->2)-beta-D-galactopyranoside and 2 as the 22-methoxy derivative of 1; 3 was deduced to be 26-O-beta-D-glucopyranosyl-22-hydroxy-5 beta-furost-25(27)-ene-12-one-3 beta,26- diol 3-O-beta-D-glucopyranosyl(1-->2)-beta-D-galactopyranoside. Preliminary pharmacological tests showed that macrostemonoside G (1) could inhibit ADP-induced human platelet aggregation in vitro (IC50 = 0.871 mM).