Abstract: The invention relates to a enzyme predicted to be a serine protease, which is specifically expressed in association with embryo implantation and placentation in pregnant uterus. The enzyme of the invention is useful in the evaluation of fertility and monitoring of early pregnancy, placental development and function, fetal development, parturition, and conditions such as pre-eclampsia, intrauterine growth restriction, early abortion, abnormal uterine bleeding, endometriosis, and cancers, and may provide a potential target for contraception. It may also be important in diseases of the heart, testis or ovary, and may play a role in muscle function, including cardiac muscle, skeletal muscle, lung and the diaphragm. In addition the enzyme of the invention is useful in the screening of candidate drugs for fertility control or for treatment of fertility-related disorders.