Sex differences exist in the functioning of the two brain corticosteroid receptor systems. Ovarian steroid replacement alters receptor mRNA expression, receptor binding capacities, and receptor affinity. The abundance of both mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) message can be reduced by estrogen. Progesterone is able to partially antagonize the action of estrogen and to induce MR transcription. The effect of estrogen on receptor binding capacity is more modest than its transcriptional actions. Estrogen decreases MR binding more reliably than it does GR. Progesterone has high affinity for the MR and can substantially reduce MR affinity for corticoids. Androgen apparently regulates corticoid receptor transcription but may not affect binding capacity. Estrogen and androgen are both more potent in regulating pituitary-adrenal function than would be suggested by their actions on receptor binding parameters.