By using [3H] cortisol and [3H] dexamethasone (DEX), a class of specific binding sites of glucocorticoids (GC) in rat liver cell membrane was observed. These binding sites had saturability, high affinity and low capacity. The kinetic parameters of [3H] cortisol and [3H] DEX were: Kd = 12.84 +/- 6.58 nmol/L (n = 4) and 40.27 +/- 23.44 nmol/L (n = 3) respectively; Bmax = 2.57 +/- 1.84 pmol/mg protein and 0.64 +/- 0.18 pmol/mg protein respectively (mean +/- SE). The Kd obtained from the kinetic studies was corresponding to the results of Scatchard analysis. Scatchard plots from the equilibrium experiments showed the straight line. The Hill coefficients were 0.9880 and 0.9990 respectively. The competitive displacement experiments indicated that cortisol possessed the higher specificity for the [3H] cortisol binding sites than other tested steroids (prednisolone, progesterone, RU486, DEX). The competitive ability of cortisol was at least 40 folds higher than mentioned steroids. By means of autoradiography technique, the existence of [3H] cortisol labelled particles on the liver cell membrane was found.