We have mapped the distribution of glucocorticoid receptor (GR) mRNA in the male adult rat brain using T7 RNA polymerase transcripts of a 1155 base pair rat GR cDNA clone comprising the coding region for amino acids 140-525. Strong expression of GR mRNA was found in the neurons of the CA1 and CA2 fields of the hippocampus and in the paraventricular and periventricular hypothalamic nuclei. Moderate to strong hybridization was found in the dorsal thalamic nuclei, layers II and VI of the cerebral cortex, the anterior olfactory nucleus and primary olfactory cortex, the hypothalamic mammillary nuclei, the subthalamus, and the granule and mitral cells of the olfactory bulb. Weak to moderate hybridization was found in many other regions of the tel- and diencephalon. Mes- and rhomboencephalic neurons displayed very low levels of GR mRNA relative to the levels observed in the tel- and diencephalon. In the cerebellum, moderate to strong levels of mRNA were detected in the granule and Purkinje cell layers with very low levels elsewhere. Nonneuronal brain elements, such as glial cells, the pia mater, and the choroid plexus, were found to express low to moderate amounts of GR mRNA. These results confirm and extend mapping studies of steroid receptors in the brain using radiolabeled steroids or monoclonal antibodies against rat liver GR and demonstrate that the relative distribution of GR protein in different brain nuclei reflects differences in GR mRNA levels. The rat GR cDNA clone is also shown to provide suitable probes for mapping GR gene expression in the mouse brain.