Dietary consumption of fish and fish oil supplements, containing eicosapentaenoic acid and docosahexaenoic acid, has been associated with favorable alterations in the cardiovascular system, such as, a reduction in blood pressure. Therefore, the effects of docosahexaenoic acid (22:6n3) on isometric tension of rat aortic smooth muscle were investigated. A concentration-dependent (1-127 microM) relaxation (6-30%) was induced by 22:6n3 in non-precontracted vessels. Docosaehexaenoic acid, concentration dependently (1-44 microM) reversed contractions of rat aortic rings induced by phenylephrine (7-43%) and by U44069 (8-52%). These results indicate that the relaxant effects produced by 22:6n3 in the rat aorta are concentration-dependent and not specific to the contractile agonist.