Prostaglandin E1(PGE1) inhibits a variety of functions of activated neutrophils including respiratory burst, release of leukotriene B4, and adherence to endothelial cells. To determine if PGE1alters the pathophysiology of complement-induced lung vascular injury, experiments were conducted in anesthetized sheep with lung lymph fistulas given a 1-hour infusion of zymosan-activated plasma. PGE, (30 ng/min/kg) or its saline vehicle was infused intravenously for 90 minutes beginning 30 minutes before the infusion of activated plasma. PGE, had no effect on leukocyte count, the initial hypoxemia and thromboxane A2release, or the development of acute pulmonary hypertension. However, PGE, prevented steady-state increases in lung lymph flow that in vehicle-treated sheep signaled an increase in lung microvascular permeability. Furthermore, extraction of PGE1by pulmonary endothelial cells was unaffected by the infusion of activated plasma. We propose that PGE1prevented the increase in lung vascular permeability by inhibiting adherence of activated neutrophils to endothelial cells.