One of several diagnostic tests to assess the integrity of the pituitary-adrenal axis, esp. used in the diagnosis of adrenocorticotropic hormone (ACTH) deficiencies and Cushing’s disease. The drug metyrapone, which inhibits the secretion of cortisol by the adrenal glands, may be given at timed intervals during the day, or as a single nighttime dose. Depending on the method of administration, plasma levels of cortisol, 11-deoxycortisol, or ACTH, or urinary levels of 17-hydroxysteroid, are evaluated to assess the patient’s response.