In Cosmos bipinnatus CAV., besides the three genes: C. I and Sp which are responsible for the expression of the cyanic and the white flower colors, there are several genes involved in the expression of the yellow coloration. When the gene C operates under dominant condition, it controls the accumulation of anthocyanins and the cyanic color of flowers, whereas under the influence of recessive alleles, white or yellow flowe]rs appear. Because the white and the yellow flowers accumulate dihydroflavonols, it is considered that the gene C expresses itself in the anthocyanin biosynthetic pathway after the appearance of dihydroflavonols while it remains to be determined whether the expression site is located before or after the flavan-3, 4-diol (1eucoanthocyanidin) step . To analyse the expression of the gene C, the flavonoids synthesized after dihydroflavonols in the biosynthetic pathway were investigated using the ray petals of four, Iines with white flowers and four lines with cyanic flowers (Table 1) in this study.