Although laparoscopic intrauterine insemination enabled fertilization to occur in lactating ewes induced to ovulate 28 days after parturition, no pregnancies were sustained when the embryos were returned to their respective post-partum uterine environments (McKelvey, Wallace, Robinson & Aitken, 1989). The incidence of inadequate luteal function, as determined by daily progesterone concentrations is high in the early post-partum ewe, yet at least 60% of ewes with an induced oestrus 21 days post-partum exhibit normal luteal function (Wallace, Robinson & Aitken, 1989). This suggests that inadequate luteal function is not the only factor limiting the establishment of pregnancy in the post-partum ewe. Indeed the transfer of good quality embryos into post-partum recipient ewes induced to ovulate 21 days after parturition and exhibiting normal luteal function failed to result in the establishment of pregnancy. This suggests that the involuting uterus of the early post-partum ewe is an inappropriate environment for embryo development (Wallace et al, 1989).