In this paper we identify the uterine epithelial cells as the site of ceruloplasmin gene expression in the uterus. We show that during the estrous cycle ceruloplasmin RNA levels change substantially reaching a maximum at estrous. In the absence of endocrine control by the ovaries, ceruloplasmin RNA is still present suggesting that this gene is constitutively expressed by the uterine epithelial cells. However, the changes in RNA level immediately after ovariectomy and during pregnancy suggest that it is also the subject of a complex regulatory system.