Feeding experiments of tobacco tissue cultures with (U)- 14 C-phenylalanine, 2- 14 C-cinnamic acid, 2- 14 C-glucosidoferulic acid and methyl- 14 C-methionine were carried out over periods from 3 min to 10 hr. The use of short feedings enabled us to study the kinetic aspect of the biosynthesis and to demonstrate the following main pathway: phenylalanine → free cinnamic acid → free p -coumaric acid → free caffeic acid → free ferulic acid → scopoletin → scopolin. Turn-over rates of free forms were shown to be much higher than those of the corresponding bound forms.