Normal human lung parenchyma, passively sensitized with an hyperimmune serum, releases eicosanoids from the cyclo-oxygenase pathway and from different lipoxygenases (5-, 12-, 15-HETE) upon anti-IgE challenge. Prostaglandin D2 represents almost 50% of the total arachidonate metabolites whereas, among sulphidopeptide leukotrienes, LTE4 is the one present in larger amounts. Pretreatment of the passively sensitized tissue with indomethacin (1.5 X 10(-5) M) inhibits cyclo-oxygenase by more than 90% without a concomitant shift of arachidonate metabolism towards leukotriene formation.