Salivary cortisol is used to confirm a diagnosis of hypercortisolism in the evaluation of patients with suspected Cushing's syndrome. The measurement is conducted late at night (11pm - 12 midnight) which is the physiological nadir for cortisol in patients with normal sleep wake cycles. Loss of this normal diurnal variation is one of the characteristics of Cushing's syndrome. Cortisol in saliva is in equilibrium with Free plasma Cortisol, biological active component. This assay is 92-100% sensitive & 93-100% specific, hence it serves as the first line test for screening of Cushing's syndrome.