The gram-negative bacteria Agrobacterium rhizogenes is a plant pathogen. On infecting plants it induces adventitious roots, known as "hairy roots." Hairy roots have an excellent growth capacity in simple culture systems without requiring the addition of any exogenous plant hormones.1,2) Furthermore, hairy roots are known to produce secondary metabolites at a high yield compared to those of undifferentiated plant cell suspensions and their mother plants. So, hairy roots were expected to provide a culture system for the production of pharmacologically important natural products and the biotransformation of organic compounds into useful biologically active compounds. Thus, many medicinal plants have been transformed to hairy roots, and there have been many related reports on the efficient production of useful natural products 3-7) and biotransformation of organic substances into useful compounds.8-10) Furthermore, hairy roots were expected to become a simple and easy experimental system for the biosynthesis of secondary metabolites such as phytoalexins, and plant gene engineering.11,12) Elicitation of hairy roots on culture with heavy metal ions such as cupper ion, organic chemicals such as jasmonic acid and biological substances such as yeast extract was studied, and found to enhance defense processes in plants and the production of secondary metabolites such as phytoalexins. 13,14) Especially, there were many reports concerning induction by plant hormones, jasmonic acid, and methyl jasmonate (MeJA). In many cases, MeJA enhanced the production of pharmacologically important secondary metabolites such as defense compounds, phytoalexins, [15][16][17] and defence systems in plants. 18) We reported the production of a coumarin-type phytoalexin, umbelliferone, in Pharbitsis nil hairy roots.19) The P. nil hairy roots also showed substrate specific and strong reactivity on the glucosylation of low-molecular-weight phenolic compounds, and strong reactivity on the reduction of a formyl group on the aromatic ring to a hydroxymethyl group. 20,21) Solanaceae, such as Solanum, Hyoscyamus, and Atropa sp., were used as medicinal plants, yielding alkaloids such as nicotine and tropan alkaloids as the main constituents, but they produced sesquiterpene-type phytoalexins, such as lubimine 22) and solavetivone, 23) after treatment with biotic and abiotic elicitors. We reported the production of sesquiterpene-type phytoallexins in Hyoscyamus albus (Solanaceae) hairy roots treated with MeJA,24) and the efficient production of tropane alkaloids in H. niger hairy roots. 25) We also reported the identification of a strongly expressed gene in H. niger hairy roots, related to and enhancing lateral root formation in H. niger hairy roots. 26) We previously found that products from H. albus hairy roots treated with CuSO 4 , MeJA, and co-treatment of CuSO 4 -MeJA showed different production patterns in terms of the TLC profile. So, we attempted to produce sesquiterpene-type phytoallexins in H. albus hairy roots cell culture by co-treatment with...