The administration of glucocorticoid combined with antiestrogen such as clomiphene has been shown to be effective for the induction of ovulation in patients with anovulation. The present study was undertaken to examine the effects of glucocorticoid on estrogen-induced changes in the pituitary gland. A single intraperitoneal (i.p.) administration of 10 micrograms estradiol-17 beta (E2) in ovariectomized and adrenalectomized rats resulted in a significant stimulation of pituitaries with regard to wet tissue weight and progesterone receptor content. An i.p. administration of 1 mg dexamethasone in these animals had no effects on both the values. However, the E2-induced increases in pituitary weight and progesterone receptor content were significantly inhibited by pretreatment with 1 mg of dexamethasone. The pretreatment with dexamethasone, on the other hand, had no significant effect on the dynamics of pituitary estrogen receptor induced by the injection of E2, i.e. the degree of nuclear translocation, occupancy and cytoplasmic receptor replenishment. The inhibitory effect of dexamethasone, therefore, does not seem to be mediated through estrogen receptor system in the pituitary. These results suggest that dexamethasone acts directly on the pituitary gland to suppress the action of E2, and which may be involved in the process of induction of ovulation by glucocorticoid-clomiphene treatment.