Estrogen, androgen, progestin, and glucocorticoid binding was measured in the immature chick bursa of Fabricius. Studies with whole bursal cytosol indicated the presence of distinct and noninteracting estradiol, dihydrotestosterone, progesterone, and dexamethasone receptors with mean dissociation constants of 0.1, 0.3, 7.8, and 12 nM and average binding site concentrations of 1.9, 13.6, 42, and 520 fmoles/mg protein, respectively. Binding to saturable sites was specific for steroids with estrogen, androgen, progestin, or glucocorticoid activity. For example, estrone and diethylstilbestrol competed with estradiol, whereas progesterone, dihydrotestosterone, and dexamethasone did not. Similarly, testosterone competed for dihydrotestosterone binding, whereas estradiol, progesterone, and dexamethasone competed very little. In the presence of 5 µM cortisol, progestosterone binding was competed for by the anti-progestin R-5020, but not by dexamethasone, estradiol, and dihydrotestosterone. Competition for dexamethasone binding was observed with cortisol and corticosterone but not with estradiol, dihydrotestosterone, and progesterone. When cytosol was prepared from bursal cell pellets that were predominantly lymphoid in nature, glucocorticoid but not estrogen, androgen, or progestin binding was identified. Since only glucocorticoid binding was found, it suggests that estrogen, androgen, and progestin receptors are present in epithelial cells of the bursa. Binding of dexamethasone in intact cells to cytosol and nuclear forms of the receptor complex and the temperature-dependent translocation of receptor complex from the cytosol to the nucleus were also shown. The results presented indicate that estrogens, androgens, progestins, and glucocorticoids interact with cells in the bursa of Fabricius at physiologic concentrations.