A Study to Confirm Recurrent or Persistent Cushing's Syndrome in Patients With Signs or Symptoms of Hypercortisolemia

Inclusion Criteria: * Are at least 18 years of age. * Have a presumptive diagnosis of Cushing's disease (Cushing's syndrome due to an ACTH secreting pituitary tumor). * Have previously had pituitary surgery and/or pituitary radiation with the intent of curing or treating Cushing's disease. * Have clinical symptoms and signs of hypercortisolism. * Are able to provide written informed consent. * Are expected to complete the study. Exclusion Criteria: * Are surgical candidates for pituitary surgery or have had pituitary surgery within 8 weeks before screening. * Have taken any medication that may interfere with protocol testing procedures within 30 days of initial screening (phenobarbital, phenytoin, carbamazepine, oxcarabazepine, primidone, rifampin, rifapentine, rifabutin, ethosuximide, pioglitazone, efavirenz, neviparine, modafinil, St. Johns wort, glucorticoids, estrogen containing oral contraceptives). * Have received investigational treatment (drug, biologic agent or device) within 30 days of screening. * Have a non-endogenous source of hypercortisolemia such as factitious hypercortisolemia (exogenous source of glucocorticoid, iatrogenic Cushing's syndrome), factitious or therapeutic use of ACTH. * Have Pseudo-Cushing's syndrome. Subjects with suspected Pseudo-Cushing's syndrome such as those with severe obesity, major depression or a history of alcoholism. * Uncontrolled, clinically significant hypothyroidism or hyperthyroidism. * Have renal failure as defined by a serum creatinine of 202 mg/dL. * Elevated total bilirubin (\>1.5x ULN), elevated ALT(\>3x ULN) or AST (\>3x ULN).