In the present study, we examined the in vivo effects of estradiol (E ₂ ) and progesterone on cyclooxygenase (COX) 2, prostaglandin F synthase (PTGFS, also known as PGFS), and membrane-associated prostaglandin E synthase 1 (mPTGES1) expression at both mRNA and protein levels using a nonpregnant ovariectomized (OVX) sheep model. Sixteen ewes were OVX shortly after ovulation. After 40 days, ewes were treated with saline (Cont, n =5), or E ₂ infused intravenously for 2 days (50 μg/day, n =5) or intravaginal progesterone (P) sponges for 10 days (0.3 g P, n =6). Cervical COX2, PTGFS, and mPTGES1 mRNA and protein were quantified by northern and western blot analyses respectively. In situ hybridization and/or immunocytochemistry were used to localize the cellular distribution of COX2, PTGFS, and mPTGES1 mRNAs and proteins. COX2 mRNA abundance increased significantly in the cervix after E ₂ treatment ( P <0.05). However, progesterone was a more potent stimulator than E ₂ of COX2 mRNA and protein abundance in the cervix ( P <0.01). In contrast, PTGFS and mPTGES1 mRNA and protein concentrations did not change after E ₂ or progesterone treatment ( P >0.05). COX2, PTGFS, and mPTGES1 mRNA and protein were only localized in cervical glandular epithelial cells. This study shows that increased cervical COX2 mRNA and protein, but not PTGFS and mPTGES1 mRNA and protein, were associated with E ₂ and progesterone treatment in nonpregnant sheep. More strikingly, progesterone was a more potent stimulator of cervical COX2 expression than E ₂ . The expression of COX2, PTGFS, and mPTGES1 mRNA and/or protein was confined in the cervical glandular epithelial cells of nonpregnant sheep.