In the rodent uterus, prostaglandin E₂ (PGE₂) is believed to have a major role in implantation and decidualization. The present study investigated the temporal and hormonal control of mRNA expression for the four E-prostanoid (EP_1–4) receptors in the rat endometrium. For Northern blot analysis and in situ hybridization, samples were obtained from rats on Days 1–10 of pseudopregnancy or from rats differentially sensitized for the decidual cell reaction with estradiol. No EP₁ mRNA signal was detected. Endometrial EP₂ and EP₃ mRNA levels increased to a maximum on Day 5, and the mRNAs were localized to the luminal epithelium at the antimesometrial pole, and in the endometrial stroma and glandular epithelium, respectively. Endometrial EP₄ mRNA levels were unchanged on Days 1–5, but the mRNA was concentrated in the antimesometrial endometrial stroma on Day 5. Cell-specific expression of EP₂, EP₃, and EP₄ on Day 5 was dependent upon a dose of estradiol given on Day 4 that induced differential uterine sensitization on Day 5. After the application of a deciduogenic stimulus on Day 5, mRNA levels for these receptors decreased significantly, while in nonstimulated horns they remained elevated. Overall, these results support a role for PGE₂ in the onset of receptivity and initiation of decidualization in the rat.