Recent studies have indicated that renal arteries can produce 20-hydroxyeicosatetraenoic acid (20-HETE) and suggest the potential involvement of a P450 metabolite of arachidonic acid in the myogenic activation of canine renal arteries. In the present study, the effects of 20-HETE on isolated canine renal arcuate arteries were studied. Administration of 20-HETE to the bath or the lumen at concentrations of 0.01–1 μMproduced a graded reduction in the diameter of these vessels. In contrast, 19(R)-HETEwas a vasodilator, whereas 19(S)-HETEwas relatively inactive. The vasoconstrictor response to 20-HETE was not altered by the cyclooxygenase inhibitor indomethacin, endoperoxide/thromboxane receptor antagonist SQ29548, or combined blockade of the cyclooxygenase, lipoxygenase, and P450 pathways using indomethacin, baicalein, and 7-ethoxyresorufin. The response to 20-HETE was associated with depolarization and a sustained increase in the intracellular calcium concentration in renal vascular smooth muscle cells. Patch-clamp studies indicated that 20-HETE significantly reduced mean open time, the open-state probability, and the frequency of opening of a 117-pS K+channel recorded from renal vascular smooth muscle cells in the cell-attached mode. Microsomes prepared from the renal cortex of dogs produced 20-HETE and 20-carboxyarachidonic acid when incubated with [14Clarachidonic acid. These results indicate that 20-HETE is an endogenous constrictor of canine renal arcuate arteries. The vasoconstrictor response to 20-HETE resembles the myogenic activation of these vessels after elevations in transmural pressure and suggests a potential role for this substance in the regulation of renal vascular tone.