Different methods were used to evaluate the effect of ATP, temperature and dilution of cytosol on the molecular properties of the glucocorticoid corticoid receptor from rat heart. Brief heat treatment of cytosol 3H-triamcinolone acetonide-receptor complexes or incubation of complexes with ATP at low temperature increased the partition coefficient of steroid-receptor complexes in the aqueous two-phase system and also nuclear uptake of the complexes. The transformation of the complexes achieved by ATP was more pronounced compared with that induced by thermal treatment or dilution of the cytosol. The activating effect of ATP on the glucocorticoid receptors was also proved by change in elution profile of the complexes from DEAE cellulose column. The effect of ATP on receptor activation was inhibited by sodium molybdate. These results suggest that activation of the glucocorticoid receptors in the intact cells may by regulated by the interaction of ATP with receptors protein itself or with another cytoplasmic plasmic component that regulates the receptor function.