This MAb is specific for progesterone. It exhibits minimal cross reactivity with related compounds in ELISA. It reacts with Progesterone-11a-HMS-BSA: 100%; 5-beta-Pregnane-3,20-dione: 48%; 5-alpha-Pregnane-3,20-dione: 26.4%; 17-alpha-Hydroxyprogesterone: 2.5% and 20-alpha-Hydroxyprogesterone: 0.04%. Progesterone is a steroid hormone synthesized from the cholesterol derivative, pregnenolone, in the cortex of the adrenal gland. Progesterone is secreted by the corpus luteum and acts to prepare the endometrium for the implantation of a fertilized egg. During pregnancy, it is secreted by the placenta to prevent spontaneous abortion and to stimulate the development of mammary tissue to produce milk. Thus, progesterone plays a central role in the reproductive events associated with the establishment and maintenance of pregnancy. Luteinized theca cells of normal ovary secrete progesterone. The determination of progesterone concentrations in the body fluids is of great value for endocrinological investigations in women. This MAb may prove useful in identification of ovarian tumors.