Glucocorticoid receptor resistance in humans occurs rarely in hereditary disorders. RU486 blocks progesterone receptors, but at higher doses also blocks glucocorticoid receptors. In this article, the clinical and biochemical effects of long-term treatment with RU486 of patients with meningiomas, breast cancer, and Cushing's syndrome are compared with those present in patients with hereditary glucocorticoid receptor resistance. The potential use of RU486 outside the field of fertility regulation is discussed.