Inhibition by prostaglandin E1(PGE1) of superoxide anion (O2) production by isolated intact human neutrophils (PMNs) was investigated utilizing initial-velocity enzyme kinetics. Lag time, linearity, rate, and extent of reaction were simultaneously examined. Dose-response data indicate progressive PGE1-induced suppression of O&OV0276; synthesis by activated PMNs with a Kivalue of 0.50 and 0.98 μmol/L for initial velocity and extent of reaction, respectively. There were no significant dose-related trends for either lag time or linearity for reactions with PGE1concentrations less than 10-6mol/L; however, at concentrations of 10-8mol/L and greater, the length of reaction was progressively shortened. PGE1inhibition of PMN-induced O&OV0276; production does not involve PMN activation/desensitization since PGE1itself cannot stimulate O&OV0276; generation. Moreover, PGE1does not function as a free-radical scavenger. These data indicate the clinical feasibility of utilizing PGE1to titrate PMN-induced synthesis of active oxygen metabolites, in order to attenuate PMN-associated host au-toinjury.