Human neutrophils rapidly undergo apoptotic cell death. Because glucocorticoids are known to modulate an array of neutrophil functional activities as well as induce rapid apoptosis in susceptible lymphocyte populations, we have examined the effects of glucocorticoids on apoptosis in mature human neutrophils. In cultures of neutrophils maintained in vitro, the glucocorticoids, dexamethasone, 6 alpha-methylprednisolone, and hydrocortisone, inhibited the development of apoptotic morphology by 59% to 90% when assessed at 12, 24, and 48 hours. In contrast, corticosteroids lacking anti-inflammatory activity and progesterone failed to affect development of the morphologic features of apoptosis. The concentration of dexamethasone required to reduce apoptosis by 50% at 24 hours was approximately 5 x 10(-8) mol/L, a concentration that is achievable in plasma after dexamethasone treatment. Dexamethasone (10(-6) mol/L), but not progesterone, reduced the percentage of hypodiploid (apoptotic) nuclei by 40% to 90% over this time course. Similarly, dexamethasone reduced the DNA cleavage associated with apoptosis and prolonged the viability of neutrophils maintained in culture for 12 to 48 hours. Glucocorticoid-mediated modulation of neutrophil apoptosis was qualitatively similar, but lesser in magnitude, when compared with the effects of granulocyte colony-stimulating factor (100 ng/mL). Thus, glucocorticoids exert a protective effect on human neutrophil survival by delaying apoptosis.