During the oestrous or menstrual cycle and throughout much of pregnancy, the uterine endometrium undergoes rapid, as well as progressive, morphological and functional modification. During the preimplantation stage of pregnancy, the endometrium provides an environment that sustains embryonic development, and then participates in the nidation process. Later, the endometrium contributes the maternal component of the fetomaternal placenta. For a successful pregnancy, the placenta must orchestrate and regulate opposing forces. Trophoblast invasion must be limited to protect the uterus from destruction, while the allogenic fetus must be guarded from maternal immunological attack. Because of their powerful effects on the cellular and molecular processes associated with cellular proliferation and differentiation, angiogenesis and immunomodulation, the transforming growth factor beta (TGF-beta) polypeptides have been identified as potential modulators of many endometrial functions. Here, we examine the literature concerning cell-specific and temporal patterns of TGF-beta expression in the uterine endometrium during the oestrous cycle and pregnancy and evaluate the influence of ovarian steroids on TGF-beta expression in a range of species. Studies of the function of TGF-beta in the endometrium and at the fetomaternal interface are reviewed and discussed.