Abstract The effects of sickle red cell-endothelial cell interaction on endothelial cell arachidonic acid (AA) mobilization, eicosanoid release, and diacylglycerol (DAG) production were evaluated by using bovine aortic endothelial cells. We have shown that coincubation of washed red blood cells (RBCs) from patients with sickle cell disease with endothelial cells stimulate AA release (90% increase as compared with buffer controls, n=8, p < 0.002). Released AA was mobilized from membrane phosphatidylcholine and phosphatidylserine and was converted to eicosanoids via the cyclooxygenase and lipoxygenase pathways in increased amounts in the presence of sickle erythrocytes. The production of prostacyclin and 15-hydroxyeicosatetraenoic acid (15-HETE) were increased by 78% ( p < 0.01) and 103% ( p < 0.025), respectively, as shown by both chromatographic and immunoassay procedures. Sickle erythrocytes also stimulated the hydrolysis of endothelial cell phosphoinositides, including phosphatidylinositol-mono-phosphate ( p < 0.03) and phosphatidylinositol-bis-phosphate ( p < 0.006). This response was accompanied by a significant increase in the production of DAG (50% increase as compared with buffer control, n=8, p < 0.025). In contrast, coincubation of washed erythrocytes from normal healthy donors with endothelial cells had no significant effect on endothelial cell phospholipid turnover. When the sickle RBC-induced biochemical changes in endothelial cells were contrasted with those observed with normal RBCs, the ability of sickle RBCs to induce AA mobilization and the production of mono-HETEs and DAG was markedly increased ( p=0.05 to p < 0.025). Because 15-HETE is a pro-adhesinogenic eicosanoid and DAG is an endogenous activator of protein kinase C, an enzyme involved in modulating cell surface adhesive properties, both 15-HETE and DAG could potentially play a role in the vascular pathophysiology of sickle cell disease.