The influence of oestradiol benzoate and progesterone on the morphological and secretory characteristics of the epithelium of the ampulla tubae was studied in ovariectomized ewes. In untreated ovariectomized animals the epithelial height is minimal, the nuclei of the secretory cells are located in the most apical part of the cells i.e. in the cytoplasmic protrusions, and secretum (PAS positive material) is not present. The only change after progesterone treatment is a slight increase in epithelial height. After treatment with oestradiol benzoate, the epithelium reacts with an increase in height and with a withdrawal of the nuclei of the secretory cells towards the basal region of the cell. Two or three days after the treatment, the amount of secretum is comparable to that during D2 or D3 of the normal oestrous cycle. It is concluded that the rise in oestrogen levels on the day prior to the onset of oestrus in a normal oestrous cycle is responsible for stimulating the biosynthetic apparatus of the secretory cell, resulting in a maximal storage of secretum two or three days after heat. Progesterone does not seem to play an important role in the release of the stored secretum; 10 days after a 3 days oestrogen treatment, the amount appears to be similar to that in animals receiving progesterone after application of oestrogen. It is suggested that release takes place as a logic consequence of synthesis without a specific trigger. The results after a combined administration of the two steroids indicate that progesterone interferes with the action of oestradiol benzoate. The apical position of the nuclei of the secretory cells during the luteal phase of the cycle must be attributed to a diminishing oestrogenic influence rather than to an active intervention of progesterone.