Chicory (Cichorium intybus L.) is traditionally recognized for its anti-inflammatory, antimicrobial, anticancer and nutritive properties. Among active secondary metabolites detected in chicory, the most important are sesquiterpene lactones and phenolics, including chlorogenic acid (CA). Hereby we have analyzed the content of CA in previously obtained Agrobacterium rhizogenes – transformed chicory hairy root cultures and transformed regenerants. Among three analyzed hairy root clones, clone 13 had exceptionally high biomass production, so the amount of CA in this culture was the highest, e.g. 400 times higher in comparison to the untransformed root culture. Since the roots spontaneously regenerated, the system was upgraded to allow the compa...