The study of daidzein derivatives provides further support to the conclusions already arrived at regarding the special features of partial methylation and demethylation in the isoflavone series. Partial methylation of daidzein gives a good yield of the 7-monomethyl ether (isoformononetin) and the formation of the isomeric formononetin could not be detected. The same 7-methyl ether is obtained most conveniently by the demethylation of daidzein dimethyl ether with hydrobromic acid and hydriodic acid. 5:7-Dihydroxy and di-methoxy isoflavones have also been examined with a view to compare them with corresponding flavones. 7-Methoxy-5-hydroxy isoflavone is obtained most readily by partial demethylation of dimethoxy isoflavone with hydriodic acid whereas chrysin dimethyl ether yields mostly chrysin under these conditions.