Abstract Incubation of [1- 14C]arachidonic acid (AA) with homogenates of bovine gallbladder muscle generated a large amount of radioactive material having the chromatographic mobility of 6-keto-PGF 1α (stable product of PGI 2) and smaller amounts of products that comigrated with PGF 2α and PGE 2. Formation of these products was inhibited by the cyclooxygenase inhibitor indomethacin. The major radioactive product identified by thin-layer chromatographic mobility and by gas chromatography - mass spectrometric analysis was found to be 6-keto-PGF 1α. The quantitative metabolic pattern of [1- 14C]PGH 2 was virtually identical to that of [1- 14C]AA. Incubation of arachidonic acid with slices of bovine gallbladder muscle released labile anti-aggregatory material in the medium, which was inhibited by aspirin or 15-hydroperoxy-AA. These results indicate that bovine gallbladder muscle has a considerable enzymatic capacity to produce PGI 2 from arachidonic acid.