PIP: To reduce the risk of IUD complications, bioelectrical activity of the cervix uteri was studied in 50 women (20-40 years old) with regular menstrual cycles. Group 1 (controls) included 10 women who did not use the IUD, and Group 2 included 40 women who used the IUD for 1-4 years. Biopotentials of the cervix uteri were studied electrophysiologically during the 1st and 2nd phases of the menstrual cycle. Electrohysterography showed normal wave-like type of bioelectrical activity in Group 1. The changes in the bioelectrical activity of the cervix uteri in Group 2 depended upon the duration of the IUD use. The women who used the IUD for 1-2 years had normal physiological activity of the uterus and ovaries (high-frequency low-amplitude biopotentials during the follicular phase, followed by an increase in their intensity during the ovulation and secretory phase of the menstrual cycle). The women who used the IUD for 3-4 years showed shortening of the luteal phase of the cycle, delay of menstruation for 5-7 days and prolongation of its duration. At electrohysterography, the high-frequency oscillations with relatively low amplitude were dominant. The intensity of biopotentials during the luteal phase was equal or slightly greater than that during the follicular phase. These findings indicated that longterm (for 4 years) use of the IUD can lead to impairment of hormonal secretion by ovaries, and that the recording of biopotentials of the cervix uteri can be used for evaluation of the functional state of the myometrium and hormonal function of the ovaries.