Cultured intact fetal membrane disks initially produced high levels of prostaglandin E2 (PGE2) on the fetal and maternal sides which declined during four days of culture. The transfer of a bolus of PGE2 from the fetal side to the maternal side of the membrane ranged from 1% to 3% after 24 hours of culture, and was a minimum over the period of 48-72 hours from the start of the incubation. To assess the handling of PGE2 synthesized by the amnion, 3H-arachidonic acid was incorporated into cultured amnion and into the amnion side of cultured intact fetal membrane disks. Labelled amnion released 3H-PGE2 on both sides of the tissue, whereas similarly labelled cultured intact fetal membrane only had detectable levels of 3H-PGE2 on the fetal side. It was calculated that no more than 9.7 +/- 1.4% of the PGE2 synthesised by the amnion crossed to the maternal side of the membrane without being metabolised during the transfer through the membrane. These results are consistent with similar indirect methods which suggested that PGE2 from the amnion may have only a limited role in human labor, and indicates the importance of using appropriate culture systems to investigate intra-uterine prostaglandin production.