Abstract: Isoflavones are modified by esterification at one or more of the C4′, C5, C6, and C7 positions to promote bioavailability, and especially to enhance solubility over the corresponding unesterified isoflavones. Preferred modifications produce a carboxylic acid hemiester or a phosphate ester which is biologically hyrolyzable. Preferred starting isoflavones are genistin and daidzin, and still more preferably comprises an aglycone form such as genistein or daidzein. Esterified isoflavones may be employed therapeutically or prophylactically for a variety of conditions, provided as a dietary supplement, or added to natural or processed food-stuffs.