The effect of brassinolide at 10-9M to 10-5M on the growth of rice seedlings was examined in darkness and under the light.After treament in darkness for one week, 10-7M and 10-5M brassinolide strongly stimulated mesocotyl and coleoptile elongation in all rice cultivars.The treatment with 10-5M brassinolide also induced the formation of the MC-type seedling, which consisted of only mesocotyl and coleoptile, the leaves being enclosed by the coleoptile.Under the light(120μmol m-2s-1, 14 h/day), brassinolide stimulated the leaf sheath elongation and increased the number of leaves.Brassinolide at 10-5M stimulated the elongation of the second leaf sheath, but inhibited that of the third leaf sheath.