We have determined eicosanoid production from endogenous arachidonic acid by neonatal lamb lungs stimulated with calcium ionophore A23187 during normoxia and hypoxia. Lungs of lambs 19 to 25 d of age were isolated and perfused with cell-free Krebs' bicarbonate buffer at a flow rate of 15 to 20 ml/kg/min. After 30 min of equilibration in a recirculating system, A23187 was added to the perfusate in a 5-microM concentration and perfusion continued for 15 min more. Eicosanoids were measured in perfusate and lung homogenate supernatant. Cyclooxygenase metabolites prostaglandin (PG) E2, thromboxane A2, and PGI2, were measured by radioimmunoassay, and 5-lipoxygenase metabolites leukotrienes (LT) B4, C4, D4, and E4 by high performance liquid chromatography. During normoxia, all three cyclooxygenase metabolites were present in perfusate, but only PGI2 and thromboxane A2 were present in lung homogenate supernatant. Prostacyclin constituted 50% of all the cyclooxygenase products measured. LTC4 and LTD4 were detected in both perfusate and lung homogenate supernatant with little production of LTE4 and LTB4. During hypoxia, the profile of cyclooxygenase products was unchanged and prostacyclin production was not increased. However, the profile of leukotriene metabolites was altered. LTC4 synthesis was markedly reduced. The synthesis of LTE4 and LTB4 was increased 10-fold, with most of the leukotrienes being retained in lung tissue. We conclude that hypoxia significantly alters leukotriene metabolism of endogenous arachidonic acid by calcium ionophore-stimulated lungs. The increased production by stimulated lungs during hypoxia of LTE4, a substance that may increase lung capillary permeability, and that of LTB4, a powerful chemoattractant, may be important contributing factors to lung injury.