Previous studies show that administration of high doses of arachidonic acid to rabbits causes disruption of vascular integrity. To examine if similar changes would occur in isolated human vascular tissue, we treated human umbilical veins with arachidonic acid (0, 0.01, 0.1, 1.0 mM). Prostacyclin biosynthesis was quantitated in the supernatants and the endothelial integrity was evaluated by scanning electron microscopy. Prostacyclin synthesis was maximum at low concentrations (0.01-0.1 mM) with no additional increase with higher concentrations of arachidonic acid (1mM) confirming previous observations. There was no evidence for endothelial disruption with any concentration of arachidonic acid. This study shows that arachidonic acid has no direct effects on the vascular lining of isolated human umbilical vein, arachidonic acid-induced sudden death in experimental animals is not due to limitation of prostacyclin synthesis.