The behavior of ciliated cells in tlie mucosal epithelium of the chicken oviduct was studied by light and scanning electron microscopy. Oviducts were collected from functionally different hens, growing pullets, and estrogen-treated pullets. The findings obtained are as follows. 1. In functiollally active laying hens, the oviductal epithelium was composed of ciliated and nonciliated cells. Both types of cells appeared to be almost equal in liumber in the magnum, uterus, and caudal infundibulum, In the isthmus and vagina, ciliated cells were predominant. Tlle cranial infundibulum and utero-vaginal juncture were covered exclusively with ciliated cells. 2. In functiollally inactive molting hens, the epithelium was deciliated markedly throughout tlle oviduct, except the vagina. Ciliated cells decreased in density to about one-half, as compared with those of the fully differentiated active oviduct. The vaginal epithelium was atrophic, but not deciliated. 3. Ciliation of tile epithelium began in the oviduct, except the vagina, at about 10 weeks of age after hatclling and was completed at about 20 weeks of age before laying. Ciliation in the vaginal epitheliunl was already noticed at 10 weeks of age and accomplished by about 15 weeks of age.