Increased menstrual loss and irregular uterine bleeding are major drawbacks to acceptibility of intrauterine contraceptive devices (IUCDs). Fibrinolytic activity around IUCDs removed from 80 women was measured by embedding the device immediately after removal in a plasminogen-rich fibrin plate. In fifteen of the women an endometrial biopsy was also taken at the time of removal of the IUCD. In women who had the IUCDs removed because of bleeding a much higher fibrinolytic activity was found than in women not complaining of excessive bleeding. The fibrinolytic activity was shown to be due to plasminogen activator and not plasmin. The findings suggest that the excessive menstrual bleeding which occurs with the IUCD may be due to enhancement of fibrinolytic activity in the endometrium which can be modified by fibrinolytic inhibitors such as epsilon aminocaproic acid.