When neutrophils are recruited to tissue sites and exposed to phagocytosable targets, they release oxidants which may be responsible for the local inactivation of alpha-1-proteinase inhibitor (AlPI). Consequently, AlPI becomes incapable of inhibiting the proteolytic activity of elastase, released at the same time by neutrophils as a result of leakage from phagocytic vacuoles. In the present paper we show that phagocytosing neutrophils inactivate AlPI via a process inhibitable by chemical agents known to interfere with the hypochlorous acid (HOCl)-generating myeloperoxidase pathway. The anti-inflammatory drug nimesulide (NMS), which is able to efficiently limit the extracellular availability of HOCl in the neutrophil surroundings, was found to prevent the inactivation of AlPI by neutrophils. The results provide evidence for a possible way to control neutrophil elastase activity by rescuing its natural inhibitor (AlPI) at inflamed tissue sites during infectious and noninfectious processes.