AVP, sometimes called Vasopressin, ADH or argipressin, is an important molecule involved in a wide range of physiological regulatory processes, including renal water reabsorption, cardiovascular homeostasis, hormone secretion from the anterior pituitary, and modulation of social behavior and emotional status. It is found in all mammals. Our assay also measures Arg8-Vasotocin which is the analogue of this hormone found in birds and reptiles. In humans, levels of AVP are between about 1 and 20 pg/mL. Our new AVP CLIA assay has a sensitivity of less than 0.9 pg/mL and is over 3-fold more sensitive than any existing assay.