Cortisol (C₂₁H₃₀O₅, hydrocortisone, compound F) is the primary glucocorticoid produced and secreted by the adrenal cortex. It is often referred to as the “stress hormone” because it is involved in body’s response to stress via affecting blood pressure, blood sugar levels, and other actions of stress adaptation. Immunologically, Cortisol functions as an important anti‐inflammatory factor, and plays a role in hypersensitivity, immunosuppression, and disease resistance. In the metabolic aspect, Cortisol promotes gluconeogenesis, liver glycogen deposition, and the reduction of glucose utilization. Production of Cortisol follows an ACTH‐dependent circadian rhythm, with a peak level in the morning and decreasing levels throughout the day. Most serum Cortisol, all but about 4 %, is bound to proteins including corticosteroid binding globulin and serum albumin. Only free Cortisol is available to most receptors and it is through these receptors that physiological processes are modulated. Abnormal Cortisol levels are being evaluated for correlation with a variety of different conditions, such as prostate cancer, depression, and schizophrenia. It is already known that abnormal levels of Cortisol are involved in Cushing’s Syndrome and Addision’s disease. The ZellX® Cortisol ELISA kit is designed to quantitatively measure Cortisol present in serum, plasma, urine, saliva, extracted dried fecal samples, and tissue culture media samples.