The secretory cells of the ampullar part of bovine oviduct are characterized by the secretory granules in cytoplasm. Their apical surface is covered with a small amount of micro-villi. Among the organellae, the Golgi apparatus is well-marked: during the sexual cycle it produces several centres. Its volume and surface reach their maxima before ovulation. The mitochondria are large and have a smaller amount of cristae. Their number culminates in pro-oestrus and their volume and surface area in metoestrus. The tubuli of granulated endoplasmic reticulum dilate during pro-oestrus and oestrus and some of them later disintegrate. They reach the largest volume and surface in pro-oestrus when the highest number of polyribosomes also occurs. Secretory granules are produced throughout the cycle as low-density spherical corpuscles covered with a simple membrane: in the course of maturation they change into high-density corpuscles and some of them break down. Their number and volume culminate in metoestrus when they are secreted on a mass scale. The population of secretory cells is heterogeneous. Besides dense and light cells, thin granules. Some cells lose contact with the basal membrane and their extrusion occurs mainly during metoestrus.