A method for selectively separating desirable steroidal glycosides from undesirable components present in plant material of the Asclepiadaceae family containing the same. The method comprises contacting the plant material or material derived therefrom (herein: "the material") with liquid or supercritical carbon dioxide under conditions whereby the desirable steroidal glycosides dissolve in the liquid or supercritical carbon dioxide in preference to the undesirable components, and subsequently recovering the desirable steroidal glycosides from the carbon dioxide solution.