COX-1 and COX-2 catalyze the production of the PG and TX precursor PGH2. COX-2 is primarily responsible for the biosynthesis of PGs under acute inflammatory conditions. The COX-1 (ovine) Inhibitor Screening Assay measures PGF2α that is produced by SnCl2 reduction of COX-1-derived PGH2. PGF2α is quantified via EIA using a broadly specific antiserum that binds to all the major PG compounds. This assay includes ovine COX-1 and is an excellent tool which can be used for general inhibitor screening, or to eliminate false positive leads generated by less specific methods.