We examined the effects of D- or L-amino acids on the stimulation of Brassica rapa roots. When 6.7 muM of D-methionine (D-Met) or L-methionine (L-Met) was applied, root hair numbers increased. L-Met (above concentration of 67.0 muM) caused the tip of roots to spiral. When CoCl2 (ethylene synthesis inhibitor) was added into the medium, L-Met lost its activity but CoCl2 did not inhibit the bioactivity of D-Met.