8-iso Prostaglandin F2β (8-iso PGF2β) is an isomer of PGF2α of non-enzymatic origin. It is one of 64 possible isomers of PGF2α which can be produced by free radical peroxidation of arachidonic acid. 8-iso PGF2β exhibits very weak contraction of human umbilical vein artery and does not promote aggregation of human whole blood. However, 8-iso PGF2β moderately contracts both the canine and porcine pulmonary vein, although the effect is much weaker than that exhibited by other isoprostanes such as 8-iso PGE1, 8-iso PGE2, or 8-iso PGF2α. 8-iso-15-keto PGF2β is a potential metabolite of 8-iso PGF2β via the 15-hydroxy PG dehydrogenase pathway. There are no published reports on the formation or biological activity of 8-iso-15-keto PGF2β.