The constitution of prunetin as the 7-methyl ether of genistein is established by preparing its diethyl ether and showing that it is identical with 7-methoxy-5 ∶ 4′-diethoxy isoflavone obtained by independent synthesis. Prunetin itself has been synthesised by a method involving partial methylation of genistein using one mole of dimethyl sulphate. The theoretical considerations are discussed. The same procedure leads to a convenient preparation of sakuranetin.