Combined quantitative polymerase chain reaction (PCR) and cytosolic binding assay techniques are used to measure mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA, K-d, and B-max in various rat central nervous system (CNS) regions, namely amygdala, hypothalamus, hippocampus, cortex, pituitary, and cervical, thoracic, and lumbar spinal cord. Two internal standards (i.s.) cDNA were cloned for quantitative PCR purposes. The i.s. templates differed from the respective wild-type (wt) templates for a single base-pair mutation introduced by PCR that generated a unique restriction site, thus allowing amplification products arising from coamplification of sol and i.s. to be distinguished. Results show that cerebellum, which displayed average B-max values for both receptors, contained the highest level of MR and GR mRNA. Hippocampus also had a high level of MR mRNA. Low mRNA content was found in the hypothalamus for MR and GR as well as in the cortex for GR. High B-max values for both MR and GR were found in the lumbar spinal cord, despite a modest mRNA content. The lowest B-max values were found in the cortex for both receptors. It is, therefore, concluded that mRNA content and B-max are not closely correlated in the rat CNS. These data suggest a differential regulation of various adrenocorticoid receptor isoforms. Moreover, this quantitative PCR method is very sensitive and can be used to assay small amounts of material in order to obtain absolute measurements of mRNA expression.