The effects of inoculum density, aeration volume and culture period on accumulation of biomass and secondary metabolites in adventitious roots of Hypericum perforatum in balloon type airlift bioreactors (3 l capacity) were investigated. The greatest increment of biomass as well as metabolite content occurred at an inoculum density of 3 g l(-1) and an aeration volume of 0.1 vvm. After 6 weeks of culture, an approximately 50-fold increase in biomass was recorded containing 60.11 mg g(-1) dry weight (DW) of phenolics, 42.7 mg g(-1) DW of flavonoids and 0.80 mg g(-1) DW of chlorogenic acid. Liquid chromatography-mass spectroscopy/mass spectroscopy demonstrated that the presence of quercetin and hyperoside in adventitious roots at a level of 1.33 and 14.01 μg g(-1) DW, respectively after 6 weeks of culture. The results suggest scale-up of adventitious root culture of H. perforatum for the production of chlorogenic acid, quercetin and hyperoside is feasible.