5-Lipoxygenase pathway-derived products of arachidonic acid released by human eosinophils activated in vitro have been measured by using radioimmunoassays specific for leukotriene B4 (LTB4) and for sulfidopeptide leukotrienes including leukotriene C4 (LTC4). Eosinophil-enriched leukocytes (mean, 85% eosinophils) from five hypereosinophilic donors activated with 5.0 pAM ionophore A23187 for 15 min at 37C in the presence of 50 mM L-serine released 69 ± 28 and 1.5 + 0.8 (mean ± SEM) ng of LTC4 and LTB4, respectively, per 106 cells; ratios of LTC4 to LTB4 ranged from 16 to 149. Eosinophils stimulated with ionophore (2.5 ,M) or phorbol myristate acetate (1 ,ug per ml) metabolized exogenously added LTC4 to products that coeluted on reverse-phase high-performance liquid chromatography with synthetic S-diastereoisomeric LTC4 sulfoxides and 6-trans-LTB4 diastereoisomers, and this metabolic inactivation was inhibited by Lserine or catalase. Ionophore-activated eosinophils purified from three normal donors also preferentially generated LTC4 (38 ± 3 ngper 106cells) relative to LTB4 (6.0 ± 3.1 ng per 106cells), whereas neutrophils from the same donors released LTB4 (48 ± 21 ng per 106 cells) in a >7-fold excess to LTC4. The predominant production by human eosinophils of LTC4 with its potent smooth muscle spasmogenic and vasoactive properties may contribute to the pathobiology of allergic and other diseases associated with eosinophilia.Human polymorphonuclear leukocytes, activated with diverse stimuli, oxidatively metabolize arachidonic acid by the 5-lipoxygenase-dependent pathway to 5,6-trans-oxido-7,9-trans-11, 14-cis-icosatetraenoic acid (leukotriene A4, LTA4) (1), which in turn is converted enzymatically to (5S,6R)-5,6-dihydroxy-6,14-cis-8, 10-trans-icosatetraenoic acid (leukotriene B4, LTB4) or to (5S,6R)-5-hydroxy-6-S-glutathionyl-7,9-trans-11, 14-cis-icosatetraenoic acid (leukotriene C4, LTC4) (2-4). LTB4 is a potent chemoattractant and aggregating stimulus for both neutrophilic and eosinophilic polymorphonuclear leukocytes (5, 6), and LTC4 is exquisitely active as a spasmogenic and vasoactive substance when administered locally to human airways and skin, respectively (7,8).Human polymorphonuclear leukocytes, predominantly neutrophils, when stimulated with the calcium ionophore A23187 produce LTB4 in marked preference to the sulfidopeptide leukotrienes, LTC4 and its peptide cleavage products (5S,6R)-5-hydroxy-6-S-cysteinylglycyl-7,9-trans -11, 14 -cis-icosatetraenoic acid (leukotriene D4, LTD4) and (5S,6R)-5-hydroxy-6-Scysteinyl-7,9-trans-11,14-cis-icosatetraenoic acid (leukotriene E4, LTE4) (2,4,9,10 diastereoisomers, and the S-diastereoisomeric sulfoxides of LTC4 were prepared as described (11)(12)(13)(14).Cell Purification. Human neutrophils were prepared from citrate-anticoagulated blood of normal volunteer donors by dextran sedimentation of erythrocytes, centrifugation on cushions of Ficoll/Hypaque, and hypotonic lysis of erythrocytes (15). Human eosinophils were obtained from the citrate-anticoagulated b...