The present invention provides a method for optimizing levels of mifepristone in a patient suffering from Cushing's syndrome. The method comprises the steps of treating the patient with seven or more daily doses of mifepristone over a period of seven or more days; testing the serum levels of the patient to determine whether the blood levels of mifepristone are greater than 1631 ng/mL; and adjusting the daily dose of the patient to achieve mifepristone blood levels greater than 1631 ng/mL.