- Male and female Cushing's syndrome aged 18-68 years with biochemically confirmed based on cortisol and ACTH measurements, dexamethasone suppression test and 1 of the following positive investigations (24 hour urine cortisol, salivary/serum cortisol profile). Visible tumour in the pituitary and/or one of the following positive tests pointing to pituitary source for ACTH overproduction (bilateral petrosal sinus sampling, corticotropin releasing hormone test, high dose dexamethasone suppression test) or adrenal tumour considered fit for surgery. No contraceptives for 6 weeks prior to sampling (females only). Patients on medical therapy e.g. metyrapone for Cushings to have a 2 week washout off treatment prior to sampling