Bioassay-guided fractionation of Gardeniae Fructus extract (GFE), which stimulates the proliferation of cultured endothelial cells, led to the isolation of glycerol and D-mannitol. Both compounds significantly increased the incorporation of [³H]thymidine and [¹⁴C]leucine into the acid-insoluble fraction of bovine aortic endothelial cell layers in culture. This clearly indicated that glycerol and D-mannitol are active components of GFE on endothelial cell proliferation. On the other hand, they did not change the number of cultured vascular smooth muscle cells from bovine aorta. Glycerol and D-mannitol may be benefical drugs for vascular disorders.