The severe loss of developmental competence affecting fertilized ova when removed from the oviductal environment suggests that this organ plays a functional role in early embryonic development. The purpose of this study was to determine the effect of sheep heat-inactivated OF on the mortality rate of ovine embryos produced in vitro and transferred into recipients. As control groups we used embryos fertilized and cultured in media supplemented with different kinds of proteins (FCS, BSA). Transfer of embryos in the two pronuclei stage to the oviducts of synchronized recipients resulted in 60% of successfully termed pregnancies after incubation of embryos in OF, 40% in BSA and only 10% after FCS. All ewes were further assessed for pregnancy by ultrasonography 33, 53 and 80 days after embryo transfer. The highest embryo mortality appeared between day 33 and 52. We concluded that incubation of ovine oocytes in OF during the final period of the maturation process may play a functional role at the time of fertilization and early embryonic development.