This review article summarizes our knowledge about three proteins associated to human pregnancy: placental protein 12 and 14 (PP12, PP14) and pregnancy-associated plasma protein-A (PAPP-A). These have in common their origin since all three seem to be produced by the pregnant endometrium (although not exclusively). Two of these proteins (PP12, PP14) have been described independently by many authors and are thus known, under many different names. For each protein their biochemical properties, their origin and regulation, their biological properties, as well as potential clinical applications, are discussed in detail. The clinical applications of PP12, PP14 and PAPP-A measurements are not only limited to uterine pathologies but also include cancer (tumour markers) and pregnancy (hydatidiform moles and extra-uterine pregnancies). This review is the first complete and comparative study of these three proteins, but many more questions are asked than solved. This is essentially due to the fact that human endometrial proteins is a rather new subject.