Inhibitory effect of colchicine on growth and gravitropic responses in Arabidopsis root was explored to find whether there was an involvement of ethylene production. It has been known that cytoskeleton components are implicated in sedimentation of statoliths to respond to gravitropism and growth. The root growth was inhibited by 25% and 40% over control for 8 hr treatment of colchicine at a concentration of 10-5 M and 10-7 M, respectively. The roots treated with colchicine at the concentration of 10-7 M showed the same pattern as control in 3 hr, however, gravitropic response was decreased in the next 5 hr. The colchicine treatment at the concentration of 10-5 M inhibited the gravitropic response resulting in 60° of curvature. In order to better understand the role of colchicine, the production of ethylene was measured with and without the treatment of colchicine. Colchicine increased the ethylene production by 20% when compared to control via the activation of ACC oxidase and ACC synthase activity. These results suggest that the inhibition of the growth and gravitropic responses of Arabidopsis roots by the treatment of colchicine could be attributed to the rearrangement of microtubule, and increase of ethylene production.