Abstract: The synthesis of daidzein, one of the active principles of Pueraria pseudohiruta, and a series of its derivatives and other isoflavones is described in this paper. The effect of these compounds on the resistance of mice to low pressure hypoxia was studied. Compounds I₂, I₁₃ and I₂₁ were shown to be more potent than the parent compound I₁ It appears that the nature of the substituent in position 4' is important for the efficacy, the alkoxy group being somewhat better. However, introduction of a methyl group in position 2 or removal of the hydroxy group in position 7 resulted in Ioss of activity.