Enzyme immunoassay for the in vitro diagnostic quantitative measurement of active free progesterone (a female hormone) in saliva. Measurements obtained by this device may be used in the diagnosis and treatment of disorders of the ovaries or placenta and can be used as an aid for prediction of ovulation. Progesterone (4-pregnene-3, 20-dione) is a C21 steroid hormone containing a keto-group (at C-3) and a double bond between C-4 and C-5. Like other steroids, it is synthesized from cholesterol via a series of enzyme-mediated steps (1) The steroid hormone Progesterone is a female sex hormone which, in conjunction with estrogens, regulates the accessory organs during the menstrual cycle and it is particularly important in preparing the endometrium for the implantation of the blastocyte and in maintaining pregnancy (2) In non-pregnant women progesterone is mainly secreted by the corpus luteum whereas in pregnancy the placenta becomes the major source (3,4). Minor sources for progesterone are the adrenal cortex for both sexes and the testes for males. The Progesterone level in saliva represents the concentration of the active free Progesterone. The DRG Salivary Progesterone HS ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA), based on the principle of competitive binding. The microtiter wells are coated with a polyclonal (rabbit) antibody directed towards an antigenic site of the Progesterone molecule. Endogenous Progesterone of a patient sample competes with a Progesterone horseradish peroxidase conjugate for binding to the coated antibody. After incubation the unbound conjugate is washed off. The amount of bound peroxidase conjugate is inversely proportional to the concentration of Progesterone in the sample. After addition of the substrate solution, the intensity of colour developed is inversely proportional to the concentration of Progesterone in the patient sample.