Cortisol (hydrocortisone, Compound F) is the major glucocorticoid hormone produced in the adrenal cortex. Cortisol is actively involved in the regulation of calcium absorption, blood pressure maintenance, anti-inflammatory function, gluconeogenesis, gastric acid and pepsin secretion, and immune function. (1,2,3) Cortisol production has a circadian rhythm. (4) Levels peak in the early morning and drop to the lowest concentration at night. (5) Levels rise independently of circadian rhythm in response to stress. (6) Increased cortisol production is associated with Cushing’s syndrome and adrenal tumors, while decreased cortisol production is associated with adrenal insufficiency (e.g., Addison’s disease) and adrenocorticotropic hormone (ACTH) deficiency. (7) In the blood only 1 to 15% of cortisol is in its unbound or biologically active form. The remaining cortisol is bound to serum proteins. (8) Unbound serum cortisol enters the saliva via intracellular mechanisms, and in saliva the majority of cortisol remains unbound to protein. (9) Salivary cortisol levels are unaffected by salivary flow rate or salivary enzymes. (10) Studies consistently report high correlations between serum and saliva cortisol, indicating that salivary cortisol levels reliably estimate serum cortisol levels. (11,12,13)