Genistein and daidzein, the major isoflavones present in soybeans, possess a wide spectrum of physiological and pharmacological functions. The bind-ing of genistein to human serum albumin (HSA) has been investigated by equilibrium dialysis, fluorescence measurements, CD and molecular visuali-zation. One mole of genistein is bound per mole of HSA with a binding constant of ± ·10 5 m )1 . Binding of genistein to HSA precludes the attachment of daidzein.