P rostaglandins (PGs) are bioactive lipids that modulate a broad spectrum of biologic processes including reproduction and circulatory homeostasis. Although reproductive functions of mammals are influenced by PGs at numerous levels, including ovulation, fertilization, implantation, and decidualization, it is not clear which PGs are involved and whether a single mechanism affects all reproductive functions. Using mice deficient in 1 of 4 prostaglandin E₂ (PGE₂) receptors — specifically, the EP2 receptor — we show that Ep2^–/– females are infertile secondary to failure of the released ovum to become fertilized in vivo. Ep2^–/– ova could be fertilized in vitro, suggesting that in addition to previously defined roles, PGs may contribute to the microenvironment in which fertilization takes place. In addition to its effects on reproduction, PGE₂ regulates regional blood flow in various vascular beds. However, its role in systemic blood pressure homeostasis is not clear. Mice deficient in the EP2 PGE₂ receptor displayed resting systolic blood pressure that was significantly lower than in wild-type controls. Blood pressure increased in these animals when they were placed on a high-salt diet, suggesting that the EP2 receptor may be involved in sodium handling by the kidney. These studies demonstrate that PGE₂, acting through the EP2 receptor, exerts potent regulatory effects on two major physiologic processes: blood pressure homeostasis and in vivo fertilization of the ovum.