Intrauterine device increases the fibrinolytic activity of the rat endometrium at deciduation, a new aspect of its contraceptive effect.

The fibrinolytic activity of the endometrium of the two uterine horns in the rat was histochemically determined. One of the horns contained a plastic-IUD, the other served as control. The endometrium of the control horn was almost inactive in contrast with that of the IUD-horn in which fibrinolytic activity was apparent. The fibrinolytic activity induced by the IUD might be involved in the prevention of ova implantation.