A mild whole body hyperthermic stress causes a rapid and reversible reduction of rat liver glucocorticoid receptor (GR) binding capacity and affects the stability of the GR-DNA complexes formed after thermal transformation of the receptor. These changes appear to be physiologically relevant, since they are accompanied by a decrease in dexamethasone induction of hepatic tyrosine aminotransferase (TAT). In spite of the decreased rate of the GR degradation in liver cytosol of hyperthermic as compared to control rats, the total amount of the GR and its proteolytic products recognized by BuGR2 monoclonal antibody was found to be lower in the former cytosol, but higher in the respective nuclei.