Abstract In the past decade, a wide variety of oxygenated metabolites of arachidonic acid have been isolated1. Most of them exhibit potent biological activity and some were also synthetized both to assess their stereochemistry and to get sufficient amounts for biological testing2. In addition to the well-known cyclooxygenase and lipoxygenase pathways, another type of metabolism was observed. NADPH dependent monooxygenation catalyzed by cytochrome P-450 induces three types of primary oxidation reactions: (a) olefin epoxidation (epoxygenase) generating four regioisomeric epoxyeicosatrienoic acids (EETs)3, (b) allylic oxidation resulting in six regioisomeric cis, trans-conjugated hydroxyeicosatetraenoic acids (HETEs), and (c) hydroxylation of an unactivated sp3 carbon (ω/ω 1 oxygenase)4.