Mating-induced endometritis (MIE) is ubiquitous in the horse after natural mating and artificial insemination with frozen/thawed semen causing the most aggressive response. The majority of mares eliminate MIE 24–48 h after insemination. An endometrial explant culture was tested as a potential in vitro exemplar for sperm-induced MIE. Endometrial prostaglandin F2α (PGF2α) secretion and expression of interleukin-8 (IL-8) were used as markers of inflammation. Endometrial explants were cultured from uteri collected from follicular phase mares. Explants were challenged with 1 or 10 × 106 sperm/ml frozen/thawed semen, chilled semen, washed sperm or seminal plasma. Medium was collected 24 and 72 h after challenge and assayed for PGF2α by radioimmunoassay. Treatment of endometrial explants with frozen/thawed, chilled semen or washed sperm did not change the secretion of PGF2α compared with untreated controls. However, 24 h after challenge cultured explants expressed IL-8. The in vitro endometrial explant system did not represent the in vivo response to semen when PGF2α was used as a marker of inflammation, yet the use of gene expression as an inflammatory marker warrants further investigation.