In vitro cultured corollas of the white flowering mutant W18 of Petunia hybrida synthesize anthocyanins after administration of a bud extract of the white flowering mutant W19. Dihydroquercetin-7-glucoside was identified as the major metabolite from W19, which is converted into anthocyanins in W18. This result supports the genetic evidences with regards to the biosynthetic pathway leading to anthocyanins in this plant. W18 was not able to convert flavanones or flavonols into anthocyanins. This type of experiments may be of value for elucidation of certain aspects of flavonoid biosynthesis.