Mechanisms that maintain high pulmonary vascular resistance (PVR) and oppose vasodilation in the fetal lung are poorly understood. Previous studies in fetal lambs demonstrate that increased pulmonary artery pressure evokes a potent vasoconstriction, suggesting that a myogenic response contributes to high PVR in the fetus. In adult systemic circulations, the arachodonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) has been shown to modulate the myogenic response, but its role in the fetal lung is unknown. We hypothesized that acute increases in pulmonary artery pressure (PAP) release 20-HETE, which causes vasoconstriction, or a myogenic response, in the fetal lung. To address this hypothesis, we studied the hemodynamic effects of N-methylsufonyl-12,12-dibromododec-11-enamide (DDMS), a specific inhibitor of 20-HETE production, on the pulmonary vasoconstriction caused by acute compression of the ductus arteriosus (DA) in chronically prepared fetal sheep. An inflatable vascular occluder around the DA was used to increase PAP under three study conditions: control; after pretreatment with nitro-L-arginine (L-NA; to inhibit shear-stress vasodilation); and after combined treatment with both L-NA and a specific 20-HETE inhibitor, DDMS. We found that DA compression after L-NA treatment increased pulmonary vascular resistance (PVR) by 44±12%. Although intrapulmonary DDMS infusion did not affect basal PVR, DDMS completely abolished the vasoconstrictor response to DA compression in the presence of L-NA (44±12% vs. 2±4% change in PVR, L-NA vs. L-NA + DDMS, p<0.05). We conclude that 20-HETE mediates the myogenic response in the fetal pulmonary circulation and speculate that pharmacologic inhibition of 20-HETE might have a therapeutic role in neonatal conditions characterized by pulmonary hypertension.