Since the mechanism of action of the intrauterine contraceptive device is still obscure, a series of experiments have been carried out using abdominal, cervical, and intrauterine electrodes, in order to record the action potentials arising in the female genital tract in the presence of such a device. Serial recordings during the various phases of the menstrual cycle from normal healthy volunteers were studied. Recordings were taken before and after introduction of an intrauterine device containing an electrode especially designed for this purpose. The recorded impulses were studied and compared in order to clarify the possible mechanism of action of the intrauterine device.