The influence of root cutting on the emergence of lateral roots was investigated in the cultures of horseradish and madder hairy roots. The original hairy roots prepared for inoculation were cut at various distances from the tips and the resultant segments were cultivated; in flasks. It was found that lateral roots very frequently emerged from the segments, depending on the longitudinal positions at which the segments were obtained. To attain the effective growth, cultivation of madder hairy roots with root cutting performed twice at 0 and 360 h was conducted. The emergence of lateral roots facilitated the growth of hairy roots owing to an increase in the number of growing points (GPs). The dry cell mass concentration and the number of GPs were 9.6 kg/m(3) and 1.9 x 10(7)/m(3) at 672 h of culture time, which were 3.6 and 4.9 times higher, respectively, than those In the control culture without the operation.