The effect of liquid flow condition on the growth of red beet hairy roots was investigated with a single-column reactor (SCR) at superficial velocities of medium ranging from 2 to 28 m/h, and the optimal growth was obtained when the superficial velocity was kept at 15 m/h in the culture for 190 h. The increase in medium flow caused the enhancement of elongation rate and decline of viability at tip meristems of the hairy roots, resulting from the enhancement of both the dissolved oxygen (DO) concentration and shear stress at hairy root surfaces, respectively. Specific cross-sectional area of bioreactor was defined as an evaluation parameter and a variation in the specific cross-sectional area was found to affect DO concentration at hairy root surfaces. Based on evaluated value of the specific cross-sectional area, a radial flow reactor (RFR) was constructed to perform the high-density culture of red beet hairy roots. Under the conditions of void fraction of hairy roots of 0.3-0.7, superficial velocity of 15 m/h and specific cross-sectional area of 40 m(-1), it was estimated that the DO concentration at hairy root surfaces increased with increasing cell mass concentration. During the culture in the RFR at superficial velocity of 15 m/h, the serious declination of DO concentration in bulk liquid did not occur owing to improvement of oxygen supply. The final density of hairy roots in a growth unit of the RFR reached 51 kg dry weight/m(3) at culture time of 280 h.