To investigate the function of microtubules (MTs) in Sertoli cell, colchicine, a microtubule disrupting agents, was injected into the dorsum of the male SD rat. The seminiferous tubules and Sertoli cell of the rat were examined by light and electron microsopy. 5-6 hours after the colchicine injection the following results were revealed (1) The Sertoli cell of the rat testis showed prominent morphological changes. The processes of the cell retracted, the MTs disappeared in the cytoplasm and the distribution of mitochondria and smooth endoplasmic reticulum became irregular. (2) Many widened intercellulor spaces occured in the seminiferous epithelium; and accordingly the arrangement of the germ cells became deranged and the elongated spermatids moved form their original deep position to the surface of the epithelium. (3) There was no evident changes in the basal region of the seminiferous epithilium. These results confirmed that MTs in Sertoli cell are essential to the maintenance of the normal shape and cellular organelle arrangement in the cell as well as the architecture of seminiferous epithelium. They may also play an important role in the movement of the elongated spermatids.