Stizolobium hassjoo hairy roots exhibited a lateral root bridging behavior, enabling not only root dry weight but enhancement of intracellular L-DOPA content. When a single root tip was exerted, a proper hindrance, the primary root growth was inhibited while lateral roots were profusely induced. The hindrance-induced lateral roots from individual primary root could bridge together under appropriate inoculation densities, leading to high density hairy root cultures producing secondary metabolites. In the present paper, a novel bioreactor was proposed based on a strategy of lateral root bridging by utilizing mesh as a hindrance, called "mesh hindrance mist trickling bioreactor (MHMTB)." Significant improvements of dry weight and L-DOPA production by using MHMTB were 1.8 and 2.2-folds, respectively, higher than those in the control run without the mesh hindrance within the root bed. (c) 2005 Wiley Periodicals, Inc.