To clarify the in vivo events following administration of steroid hormones, the effect of molybdate on the cytoplasmic glucocorticoid receptor (GR) translocation in rat livers after administration of glucocorticoids was examined. After injection of hydrocortisone-succinate (Hydro) (200 micrograms/150 g rat) into the inferior vena cava of adrenalectomized rats, 3H-dexamethasone (3H-Dex) binding in liver cytosol rapidly decreased within 5 min, followed by a rapid replenishment. This decrease in binding was partially prevented by pre-treating the animals with 20 mg of sodium molybdate (Mo), which was considered to inhibit GR activation. Administration of 200 micrograms/150 g body weight of hydrocortisone caused a rapid replenishment of the binding sites following the depletion. Administration of molybdate 5 min after the hydrocortisone injection did not influence the replenishment. The GR content was increased significantly 20 min after the administration of molybdate in intact rats but not in adrenalectomized rat. It is concluded that activation of the hormone receptor complex observed in vitro also occurs in vivo after administration of glucocorticoid to animals.