Ultrastructural details of prepubertal porcine uterine tube (oviduct) were studied in normal, growing gilts and compared with observations reported in other species. Tissues from the ampulla region of uterine tube were taken from 6 prepubertal gilts (106 to 139 days old) to determine cytodifferentiation of ciliated and secretory cells. The epithelium consisted of 2 distinctive cells, the ciliated and the secretory cells. Cilia were observed in the uterine tube of prepubertal gilts; however, degeneration of cilia was not observed in the present study. Most prominent observations were the occurrence of fibrous granules in the apical cytoplasm of ciliated cells. These fibrous granules contained electron-dense material and were present near basal bodies. The most unusual feature was the occurrence of procentrioles around a condensation form. These data indicate that ciliated cells are sensitive to estrogen. Intimate morphologic association between fibrous granules and basal bodies indicate that fibrous granules might provide precursor material for the development of cilia and rootlets. The cytoplasm of the secretory cells contained rough endoplasmic reticulum of tubular form and numerous ribosomes. Evidence for synthesis, storage, and release of secretory granules was not apparent. It is suggested that the secretory cells are not sensitive to the low, circulating concentration of plasma estrogen. The ultrastructure of the stromal cells and lymphatic capillary was described for the 1st time. The uterine tube stromal cells were characterized by prominent nucleus and a few cytoplasmic organelles. The lymphatic capillaries were distinguished by the blood capillaries, their much wider lumen, endothelium with an attenuated cytoplasm, absence of basal lamina, and overlapping and interdigitating intercellular junctions. The fine structure of the porcine uterine tube lymphatic capillary generally resembled that of other mammalian species.