Here we have examined the enzymes cyclooxygenase (COX)-2 and 15-hydroxyprostaglandin dehydrogenase (15-OH PGDH) in pregnant human cervix. In biopsies taken transvaginally after preterm and term elective cesarean sections and vaginal deliveries, the levels of mRNA coding for COX-2 and 15-OH PGDH were assessed by Northern blotting. The cellular localization of the COX-2 and 15-OH PGDH proteins was determined by immunohistochemical analysis. COX-2 and 15-OH PGDH mRNAs were expressed at detectable levels in the cervical biopsies from all four groups of subjects. At cesarean sections (unripe cervix), the level of 15-OH PGDH mRNA was significantly higher than the level in the ripe cervix at the time of partus, irrespective of the gestational length. In contrast, the level of COX-2 mRNA was similar in all subjects. Immunoreactivity of COX-2 and 15-OH PGDH was expressed by activated fibroblasts. The present investigation documents the expression and cellular localization of COX-2 and 15-OH PGDH in the preterm and term pregnant human cervix. This observation indicates that both preterm and term cervical ripening is associated with decreased degradation of prostaglandins.