Agrobacterium rhizogenese can induce hairy root phenotype in many dicotyledonous plants via the transfer of rol genes into the plant genome. The characteristics of induced roots such as a rapid growth, high stability of genetic material, ease of conservation and their ability to grow in a hormone-free medium have led to their use in the production of secondary metabolites. In the present study, we have investigated the effect of rol genes, particularly the rolB gene, on root induction of three medicinal plants valeriana officinalis, Echinacea angustifolia and Foeniculum vulgare. Leaf explants and wounded parts of stems were inoculated with bacterial suspension and the presence of bacterial DNA as well as its expression in induced roots was demonstrated using PCR and RT-PCR techniques with rolB specific primers. The results showed that maximum rooting occurred with Valeriana officinalis leaf explants cultured in MS medium and the wounded parts of stems did not show rooting at inoculated areas.