A simple suture intra-uterine device (IUD), occupying almost the entire length of the uterine horn, was used to study the effect of an IUD upon conception in the rabbit.After being mated, rabbits were killed at 84, 132, 156 and 180 hr and at 14 days. Additional animals were examined at 14 days after the IUD had been removed 84, 132 and 156 hr after mating.The IUD was not completely contraceptive, but it induced considerable pre-implantational embryonic death between 156 and 180 hr after mating.