A mixture of monoacetyldiglycerides was newly isolated from the chloroform extract of antlers of Cervus nippon, guided by the hematopoietic stimulation of stem cells. The structures of monoacetyldiglycerides were determined by various spectroscopic methods: FAB MS, CID tandem MS, and 1D and 2D NMR. A mixture of at least nine inseparable sn-3-monoacetyldiglycerides was identified: 1 [C(39)H(72)O(6) (C16 : 0/C18 : 1)], 2 [C(39)H(72)O(6) (C18 : 1/C16 : 0)], 3 [C(39)H(70)O(6) (C16 : 0/C18 : 2)], 4 [C(39)H(70)O(6) (C18 : 2/C16 : 0)], 5 [C(41)H(74)O(6) (C18 : 0/C18 : 2), 6 [C(41)H(74)O(6) (C18 : 2/C18 : 0)], 7 [C(41)H(74)O(6) (C18 : 1/C18 : 1)], 8 [C(43)H(74)O(6) (C18 : 0/C20 : 4)], and 9 [C(43)H(74)O(6) (C20 : 4/C18 : 0)]. Among these nine monoacetyldiglycerides in deer antlers, compound 3 was one of the major compounds and was efficiently synthesized from glycerol. Spectral data of synthetic monoacetyldiglyceride 3 were compared with the corresponding data for the mixture of natural monoacetyldiglycerides. The mixture of natural monoacetyldiglycerides from deer antlers showed potent activity on the hematopoiesis (stimulation index=1.40+/-0.05, p<0.02 at 1 microg/ml), and synthetic monoacetyldiglyceride 3 showed even better activity (stimulation index=1.54+/-0.12, p<0.001, at 1 microg/ml).