Fluprostenol is a metabolically stable analog of PGF2? with potent FP receptor agonist activity.{3160,1374} The isopropyl ester of fluprostenol has recently been approved for use as an ocular hypotensive drug for the treatment of glaucoma and is sold under the Alcon trade name Travoprost.{8839,9613} Acting as a prodrug, Fluprostenol isopropyl ester is converted by esterase activity in the cornea to yield the corresponding active free acid, (+)-fluprostenol.{1107} Fluprostenol is also used in the veterinary field for the induction of estrus in livestock. Cayman’s Fluprostenol ELISA is a sensitive detection method for measuring the free acid form of fluprostenol. The assay also detects the isopropyl ester form of fluprostenol, but with less sensitivity. Samples containing a mixture of the isopropyl ester and free acid should be purified and the compounds separated prior to analysis. The assay has been validated for use in aqueous humor samples.