The effects of ovariectomy at day 8 of pregnancy were studied on the granulated metrial gland cells of the mouse uterus, with and without subsequent progesterone replacement. By one day after the ovariectomy the fetuses were dead and there was extensive decidual necrosis. Though numerous granulated cells were still present after one day, accompanied by an extensive polymorphonuclear leucocytosis in the mesometrial triangle, granulated cells virtually disappeared within three days. In animals injected with 1 mg progesterone twice daily over five days, starting at the time of ovariectomy, the pregnancies survived. There was no decidual necrosis, and the numbers, morphology and distribution of the granulated metrial gland cells were normal. In ovariectomised animals injected with 0.5 mg progesterone twice daily most implantation sites after three, four and five days were associated with fetal death, though numerous granulated metrial gland cells survived. In implantation sites where the fetus had survived to thirteen days, there were markedly fewer granulated cells than in implantation sites either from control animals or from animals treated with the higher dosage of progesterone. Cytoplasmic granules in stromal cells of the metrial gland were prominent in the ovariectomised animals. They were much less numerous in animals given the lower dosage of progesterone and absent from those given the higher dosage.