Oxygenation reactions involving arachidonic acid generate biologically-active mediators. Three pathways have been described. Much attention has been focused on the products of the cyclo-oxygenase and lipoxygenase pathways but gastrointestinal pharmacologists have paid less attention to the products of the "third" pathway - the epoxygenase pathway. Metabolism by the cytochrome P450-dependent monooxygenase system occurs in three ways:(a) epoxidation producing (5,6-), (8,9-), (11,12-), and 14,15-epoxyeicosatrienoic acids (EETs), (b) allylic oxidation, resulting in the formation of (5-), (8-), (9-), (11-), (12-), and15-hydroxyeicosatetraenoic acids (HETEs) and (c) hydroxylation leading to the formation of (19-) and 20-HETES, and 20-carboxyl arachidonic acid. These products can be biologically active. This review will summarise current information and highlight potential roles in modulating intestinal ion transport. ( Supported by MRC Canada)