0.1-0.3 M sodium thiocyanate greatly enhanced the rate of inactivation of unbound rat hepatic glucocorticoid receptors in vitro at 4 degrees C. Prior treatment of the unbound glucocorticoid receptor with 10 mM molybdate (at 25 degrees C for 30 min) protected the receptor from 0.3 M KCl, but not from 0.3 M NaSCN inactivation. When the [3H]dexamethasone-receptor complex was examined on sucrose density gradients containing 0.1 M NaSCN, the receptor sedimented as a 4 S complex rather than the 7 S form observed in 0.1 M KCl gradients. NaSCN was found to be more effective in the extraction of both in vivo and in vitro nuclear-bound [3H]dexamethasone-receptor complexes than KCl. At a concentration of 0.3 M, NaSCN extracted most of the specific nuclear-bound receptor. 50 mM NaSCN significantly blocked the thermal activation of preformed [3H]dexamethasone-receptor complexes. The chaotropic salt, NaSCN, appears therefore to have significant effects on glucocorticoid receptors in vitro. In addition, NaSCN appears to be a useful agent in quantitative extraction of steroid from nuclear-bound steroid-receptor complexes.