Glucocorticoid binding to cytoplasmic and nuclear fractions and glucocorticoid-receptor complex binding to the nuclear fraction were investigated using rat liver. The glucocorticoid-receptor complex binding to the nuclear fraction was temperature-dependent, saturable, small in amount and of high affinity. The affinity and number of the glucocorticoid-receptor complex binding to the nuclear fraction were altered according to the glucocorticoid. Both the Bmax of nuclear glucocorticoid-receptor complex binding and the affinity of glucocorticoid to the cytoplasmic fraction were correlated with the relative anti-inflammatory potencies of glucocorticoids reported by Hynes and Murad (1980) and Fried et al. (1958). These results suggest that the number of nuclear binding sites of the glucocorticoid-receptor complex depends on the ligand steroid which is bound to the receptor of the cytoplasmic fraction and may be involved in physiological and pharmacological potencies of the glucocorticoid in addition to the affinity of the glucocorticoid to the receptor.