The glucocorticoid receptor in rat liver cytosol was studied by sucrose gradient sedimentation, DEAE-Sephadex A-50 column chromatography and DNA-cellulose binding in order to assign specific hydrodynamic properties to both the unactivated and the activated glucocorticoid--receptor complex with [3H]-dexamethasone. Activation was effected by heat, NaCl (0.4 M) or KSCN (0.1 M) treatment. The state of activation was judged by both DNA-cellulose binding and DEAE-Sephadex A-50 anion exchange chromatography. In isotonic phosphate buffer, unactivated and activated glucocorticoid--receptor complex sedimented as a 5 S and a 4 S peak, respectively. This 5 S-4 S transformation was blocked by sodium molybdate. In hypotonic phosphate buffer, both the unactivated and the activated glucocorticoid--receptor complex assumed higher s values due to aggregation. The activated complex (4 S) yielded aggregates of 5-6 S in a reversible manner, neither complex being affected by sodium molybdate. The unactivated complex was shown to assume two distinct aggregation states of 6 S and 8-9 S, which yielded a 10-11 S heavy aggregate upon addition of molybdate. This effect on the unactivated glucocorticoid--receptor complex was readily reversed by removing the molybdate. Aggregation at low ionic strength was promoted by a low mol. wt. component(s), separated from cytosol by gel filtration through Sephadex G-10. The state of aggregation had no pronounced effect on the DNA binding properties of the activated forms or on the sensitivity of the unactivated forms to molybdate.