Growth and diterpenoid accumulation (salvipisone, ferruginol, aethiopinone and 1-oxoaethiopinone) during the growth cycle of a Salvia sclarea hairy root culture are described. The roots transformed by Agrobacterium rhizogenes (LBA 9402) were cultured in half-strength B5 liquid medium supplemented with 30 g L Ð1 sucrose under light (16 h/8 h light/dark). A culture period of 30 days was optimal for both biomass and diterpenoid production. The total content of four diterpenoids in the hairy roots [(27.3 ð 0.6) mg g Ð1 dry weight] was higher than that of roots of field-grown S. sclarea plants [(3.15 ð 0.15) mg g Ð1 dry weight]. In transformed roots, aethiopinone was the main diterpenoid, whereas the principal diterpenoid of natural roots was salvipisone.