Sex steroids, i.e. progesterone (P 4 ) and 17β-estradiol (E 2 ), fluctuate during the feline estrous cycle and their alterations correspond to many events in cat reproduction. In order to investigate possible effects of sex steroids on prostaglandin (PG) secretion in the cultured endometrial cells, mRNA expressions coding for PG-endoperoxide synthase (PTGS2) in the epithelial and stromal cells harvested with sex steroids were studied by RT-PCR. The effects of ovarian steroids on PG secretion in the epithelial and stromal cells were also investigated. E 2 at a dose 10 -7 M significantly increased prostaglandin F2α (PGF 2α ) secretion in the epithelial cells (P<0.01). PGF 2α production was intensified by the treatment in combination with both steroids (P<0.001). P 4 at any dose alone had no effect on PGF 2α secretion in the epithelial cells, whereas at a dose 10 -5 M enhanced prostaglandin E2 (PGE 2 ) production (P<0.05). The ovarian steroids stimulated both PGF 2α and PGE 2 in the epithelial cells of the feline endometrium via an E 2 receptor (ESR1)- and P 4 receptor (PGR)-dependent genomic-pathway. In contrast to the epithelial cells, neither P 4 nor E 2 affected PG secretion in the stromal cells. PTGS2 mRNA expression was not affected by ovarian steroids in either cell types. The overall results suggest that PG secretion is regulated by P 4 and E 2 and this effect is not due to changes in PTGS2 mRNA expression.