Tumor necrosis factor-alpha (TNF), originally identified as an inflammation-associated cytokine, is synthesized throughout the female reproductive tract as well as in placentas and embryos. Development, female sex steroid hormones, and lipopolysaccharide influence expression of this gene. The functions of TNF may be determined in part by differential expression of the two species of TNF receptors, both of which seem to be regulated by female sex steroid hormones. Evidence has accumulated that supports a role for this potent, pleiotropic cytokine in autocrine and paracrine processes central to reproduction, including gamete and follicle development, steroidogenesis, uterine cyclicity, placental differentiation, development of the embryo, and parturition.