The glucocorticoid receptor population of the androgen-dependent levator ani-bulbo cavernosus muscle complex in response to both androgen withdrawal and androgen replacement was examined in rats. After castration the concentration of receptor sites more than doubled. The increase in the sites began within the first 24 h after castration and reached a plateau level within 7 days. Parallel dry weight studies demonstrated that no loss in muscle mass is observed until 48 h after castration. In a second series of experiments, both the regrowth of the muscle and the number of receptor sites in response to androgen injections were examined. By day 11 of injection, the muscle had increased in dry weight to a point where it was equal to the size of this muscle in normal intact male controls. During this process, the concentration of receptor sites began to decline 5 days after the beginning of injections and reached control or below control values by 11 days.