The autoradiographic distribution of glucocorticosteroid binding sites in the brain of adrenalectomized rats was studied following in vivo injection of a potent synthetic glucocorticosteroid agonist [3H]RU 28362. Analysis of the autoradiograms revealed a specific and dense labeling in the pyramidal cell layer of the Ammon's horn and in the granular cell layer of the dentate gyrus of the hippocampus. In the hypothalamus, the labeling was particularly high in the paraventricular nucleus (site of CRF synthesis), the arcuate, periventricular and the supraoptic nuclei as well as in the median eminence. Autoradiograms also revealed the presence of [3H]RU 28362 binding sites in several brain regions including the amygdala, the pineal gland, the entorhinal cortex, the interpeduncular, interfascicular and dorsal raphe nuclei, the central grey and the substantia nigra suggesting possible effects of glucocorticosteroids in these structures.