Cortisol is the major glucocorticoid which is secreted by the adrenal cortex. Ten to twenty mg per day of cortisol are produced. The great bulk of plasma cortisol circulates in bound form, less than 10% of serum cortisol occurs in the physiologically active free form and is excreted un-metabolized in the urine. Cortisol secretion follows a diurnal pattern with high concentration in the morning.