Purpose: We sought to determine the effect of dietary -3 polyunsaturated fatty acids enhances endotheliumdependent relaxations in the basilar artery by two mechanisms: 1) replacement of endogenous arachidonic acid and suppression of the concomitant release of vasoconstrictor prostaglandins from the endothelium, and 2) enhancement of the release of endothelium-derived relaxing factor. (Stroke 1992;23:407-413) KEY WORDS • basilar artery • endothelium-derived relaxing factor • fatty acids, unsaturated • pigs T he dietary intake of large amounts of marine oils rich in w-3 polyunsaturated fatty acids probably accounts for the low incidence of coronary artery disease among Greenland Eskimos.1 High contents of (o-3 polyunsaturated fatty acids, especially eicosapentaenoic acid, are found in the plasma and platelets of Eskimos.2 ? Eicosapentaenoic acid is transformed into trienoic prostanoids, such as thromboxane A 3 and prostaglandin I 3 .4 -6 Thromboxane A 3 does not possess proaggregatory activity, unlike the dienoic prostanoid thromboxane A 2 , 7 and prostaglandin I 3 has effects comparable to those of prostacyclin.5 Hence, supplementation with (o-3 fatty acids inhibits platelet aggregation and prolongs bleeding time, presumably due to the decreased production of thromboxane A 2 . 8 Previous studies demonstrate that dietary supplementation with cod-liver oil or purified co-3 fatty acids augments endothelium-dependent relaxations in isoFrom the Department of Physiology and Biophysics (P.K., H.S.), Mayo Clinic, Rochester, Minn., and the Center for Experimental Therapeutics (P.M.