In several mammalian species, the epithelial secretory cells of the oviduct synthesize and secrete specific glycoproteins that become associated with the zona pellucida of the ovulated oocyte. These glycoproteins are collectively designated as oviductins. A monoclonal antibody directed against hamster oviductin was used to study the ontogeny of this glycoprotein. Indirect immunof luorescence experiments performed on sections of hamster oviduct revealed that the glycoprotein begins to be secreted in 10-day-old females and that all of the oviductal secretory cells showed fluorescent staining by day 14. The intensity of the immunofluorescence reaction reached a maximum in the 28-day-old females. The oviducts of the 7-day-old hamster incorporated [35Slmethionine in vitro into several proteins; however, the production and secretion of detectable amounts of radiolabeled oviductin only began at 14 days of age and reached a maximum at day 28 of age. It appears that the ontogeny of oviductin parallels the hormone dependent changes leading to sexual maturation and that its maximum secretion is already established at the time of the first ovulatory cycle. These results are substantiated by the fact that the production of oviductin is induced in estradiol-treated, but not progesterone or non-treated prepubertal animals, as determined by indirect immunof luorescence experiments. o 1995 Wiley-Liss, Inc.