Stress or elevated corticosterone titers can reduce the concentration of corticosterone receptors in the brain. We demonstrate that corticosterone and the related glucocorticoid, dexamethasone, induce different anatomical patterns of such 'down-regulation'. Corticosterone administration reduces receptor number in the hippocampus, particularly the CA1 and CA2 pyramidal cell fields, but nowhere else in the brain or pituitary. In contrast, equivalent dosages of dexamethasone down-regulate pituitary, amygdaloid and hypothalamic corticosterone receptor numbers. These different anatomical profiles of sensitivity to down-regulation appear due to differential access of the two steroids to the receptor pools.