Cortisol is an adrenal hormone which is directly related to the body's stress response. Cortisol affects numerous physiologic systems including immune function, glucose regulation, vascular tone, and bone metabolism. Due to the normal daily fluctuations in cortisol levels, distinguishing normal from abnormally low cortisol levels can be difficult, therefore several daily collections are recommended. Separate saliva samples are collected at approximately the following four time points on the same day: (1) Immediately after you awake (6 to 8 AM) (2) Noon (3) 4 PM (4) 10 PM. *