The addition of molybdate to rabbit liver cytosol increased significantly the affinity of the glucocorticoid receptor for [3H] dexamethasone without influencing the concentration of binding sites. This effect was concentration dependent. Analysis of the binding data by curve-fitting and Scatchard plot revealed the occurrence of a complex binding process in the presence of molybdate. The pH-dependence curve of the binding was shifted towards alkaline values by the oxyanion. Taken together, these data suggest that molybdate exerts its effects via an interaction with the receptor molecule.