Estrogen and progesterone cytoplasmic receptors (ER, PgR) were determined by radiochemical DCC technique in the endometria of 16 normal women at before child bearing age and 6 to 9 months after LNG IUD insertion. The study showed that both ER and PgR were reduced significantly after LNG IUD insertion (P less than 0.01). The decrease of ER and PgR might play an important role in gland reduction and endometrial atrophy. It may be one mechanism of the contraceptive effect and the cause of anemia or spotting between menstruation during the course of LNG IUD insertion.