Human nentrophils play a pivotal role in acute inflammation. However, their capacity to generate bioactive kinin peptides has not been established as yet. We have examined the ability of neutrophil enzymes to release biologically active kinins in vitro from purified human H- and L-kininogens. Neutrophils isolated from human blood were stimulated with f-Met-Leu-Phe, thrombin, or human immunoglobulin G adsorbed to silica particles. Supernatants were incubated with iodinated kininogens, and polyacrylamide gel electrophoresis analyzed aliquots taken after a range of incubation times. A time-course analysis demonstrated that supernatants from stimulated neutrophils caused a rapid hydrolysis of both substrates, resulting in an accumulation of fragments ranging from 20 to less than 10 kDa. Radioimmunoassay (RIA) revealed that all supernatants were able to generate kinins in vitro. High-performance liquid chromatography of the generated peptides indicated that they had a retention time similar to that of bradykinin and Met-Lys-bradykinin, clearly recognized as kinin peptides when the corresponding fractions were tested by RIA. The kinin-immunoreactive fractions produced lowering of blood pressure and a dramatic increase in venular permeability. Biological activity of the neutrophil-generated kinins was completely abolished by the B2 receptor antagonist HOE140, indicating that over the time-course of the experiments, only kinin B2 agonists appeared to have been generated mid that cellular actions of these were mediated by kinin B2 receptors. Together, our results demonstrate that human neutron phil proteases can release kinins from both plasma kininogens, suggesting that these peptides may participate actively during acute in-flannuation.