Artificial programming of the menstrual cycle in rhesus monkeys is a remarkable advance in primate uterine biology (Hodgen, 1983). Ovariectomized mature monkeys receive subcutaneous silastic implants of estradiol and progesterone that mimic the serum steroidal hormonal profile of a natural 28-day menstrual cycle. Transfer of surrogate preimplantation embryos into the ampulla of the fallopian tube during artificial cycles has resulted in successful pregnancies and birth of normal offspring. This achievement was followed by production of fertile cycles in women who had been ovariectomized or had primary ovarian failure (Lutjen et al., 1984; Navot et al., 1986). These fundamental demonstrations established that primate uterine cyclic growth depends primarily on an appropriate pattern of systemic estradiol and progesterone secretion.