The effects of orchiectomy have been observed, with SEM, on the vas deferens and seminal vesicles epithelium of 20 adult albino rats. The inner surface of castrated rat vas deferens shows a reduction in height and thickness of the mucosal folds and, at the cellular apex, a remarkable decrease of the microvilli as well as the disappearance of the secretory blebs. At the level of the seminal vesicles also, castration affects both the mucosal folds, which are flattened, and the cellular apical features, with the reduction of the microvilli and the disappearance of the secretory granules. Such changes give evidence in favour of a decrease in the absorptive capacity and a suppression of the secretory activity of these epithelia, as a consequence of the fall of androgen levels.