Abstract: The flavonoid family of phytochemicals, particularly those derived from soy, has received attention regarding their hormonal activity and their effects on human health and disease. The types and amounts of these compounds in soy and other plants are controlled by both constitutive expression and stress-induced biosynthesis. The health benefits of soy may therefore be dependent upon the amounts of the various hormonally active phytochemicals present. We have identified increased biosynthesis of the isoflavonoid phytoalexin compounds, Glyceollins I, II and III, in soy plants grown under stressed conditions (elicited soy), which exhibit marked anti-estrogenic effects on ER function.