It is known that prostaglandin (PG)E2 and PGI2 can contribute to the ripening of the uterine cervix. To study the PG biosynthesis in cervical tissue, 14C-arachidonic acid was used to incubate the preparation of human cervical tissue obtained from pregnant women at delivery and non pregnant women at hysterectomy. Labeled PGE2 and 6-keto-PGF1 alpha (6PG), a stable metabolite of PGI2 were isolated on TLC, and the enzymatic activity was calculated from the formation of PGE2 and 6PG from arachidonic acid. The capacity to metabolize arachidonic acid to PGE2 and 6PG in cervical tissue obtained from pregnant women was 6 times higher than that from non pregnant women. Low enzymatic activity in the formation of PGE2 and 6PG were observed in cervical tissues from the patients with placental sulfatase deficiency and preterm delivery which were known to have a low estrogen environment. On the other hand, DHA-S administration to patients increased the formation of both PGE2 and 6PG. These results demonstrate that human cervical tissue possesses the ability to synthesize PGE2 and PGI2, and enzymatic activity increased during pregnancy, and was further enhanced by the administration of DHA-S. The results suggest that the steroids in the fetoplacental unit may be involved in the mechanism controlling the formation of PGs in the cervical tissue which lead the cervix to ripen at term.