With the aid of DL-phenylalanine- [carboxyl-14C] it has been demonstrated that the carbon skeleton of phenylalanine is incorporated into 7-hydroxy-4-methoxy-iso-flavone (formononetin) in red clover and that a rearrangement takes place. The isotope distribution found can be explained by a migration of either a phenyl or a benzoyl group in the course of the biogenesis. A biogenetic scheme is presented which explains the formation of all flavones, iso-flavones and coumestrol found in red clover.