We have determined binding sites for estrogen, progestin, androgen and glucocorticoid in anterior pituitaries from Sprague-Dawley rats, a strain with low estrogen sensitivity, and in diethylstilbestrol-induced pituitary tumors in Fischer 344 rats, a strain with high estrogen sensitivity. Binding sites differ in their quantity and subcellular distribution. Cytosolic sites for [3H]estradiol in normal pituitaries from untreated rats were high prevailing over sites for other hormones, but they were depleted in the tumors due to their retention in nuclei under the influence of estrogen. Unoccupied nuclear sites for estrogen in normal glands also prevailed over sites for other steroids, and were similar to those in tumors. Second, the progestin site labeled with [3H]R 5020 was concentrated 5.7-fold in cytosol and 8.5-fold in nuclei of the tumors over the values found in glands from normal males estrogenized for 3 days. Third, glucocorticoid receptors labeled with [3H]dexamethasone were predominantly cytosolic in normal glands, but very low in cytosol and more evident in nuclear extracts from the tumors, the reverse of the profile found in normal pituitaries. Last, limited and comparable amounts of androgen receptors were measured in the subcellular fractions of both tissues. It is suggested that the subcellular distribution of some steroid receptors may be controlled in part by the cell population of the tissue and its degree of genetic activity.