To date the main limitation of in-vitro fertilization-embryo transfer (IVF-ET) programmes is that transcervical transfer of embryos results in a rate of low implantation. On the other hand, the technique of gamete intra-Fallopian transfer (GIFT) does not contribute to information on oocyte fertilization rates, and the time of oocyte exposure to sperm may be limited. The development of ultrasonically guided follicular aspiration will allow transfer of embryos generated in vitro to the Fallopian tubes performing only one surgical procedure in the process. We have performed 25 intra-tubal embryo transfers in the cynomolgus monkey (Macaca fascicularis). Ovarian stimulation, follicular aspiration and IVF procedures have been reported previously by Balmaceda. ETs were performed via laparotomy. Embryos at the 2-, 4- or 9-cell stage were loaded into a tom-cat catheter in 5 microliter of culture medium and delivered to the mid-ampullary portion of the tube. Seven ETs performed during stimulated cycles resulted in one pregnancy, and 18 ETs performed in synchronized recipients resulted in six pregnancies. Ten ETs were performed 0-24 h, eight performed 24-48 h and seven performed 72-110 h after follicular aspiration or ovulation, and resulted in 4, 3 and 0 pregnancies respectively. Our results demonstrate that intra-tubal embryo transfer can result in normal intra-uterine pregnancies and suggest that both ovarian stimulation and cycle synchronization affect the probability of embryo implantation.