Adding epidermal growth factor (EGF) stimulated the fibroblast proliferative effect of SSb1 and SSb2. Consequently, fibroblast proliferative effect appears to be associated with the presence of a double bond at C-13 or hydroxymethylene group at C-17 within the chemical structure of those five saikosaponins, as SSb1 and SSb2 were metabolized by the cleavage of the 13-ether bond of SSa and SSd respectively.