Human neutrophil elastase (HNE, EC 3, 4 21, 11), a major causative factor in the induction of pulmonary emphysema, were purified by two steps of liquid chromatography. Purified elastases were cross-reacted with antibody to human neutrophil elastases. Methicillin and cefamandole, which are known as inhibitors of cell wall synthesis of microorganisms, could inhibit the activity of human neutrophil elastase up to 50% with 10mM of both agents and IC50 of methicillin was 9.8 mM. Gentamicin, one of the aminoglycosides, also inhibits human neutrophil elastases up to 60% of original activity with 10 mM of this agent and IC50 was 9.0 mM. We could demonstrate similar effects in oxytetracycline. 10 mM of oxytetracycline inhibited 95% of human neutrophil elastase and IC50 was 0.3 mM. Overall, oxytetracycline, cefamandole and methicillin are strong inhibitors of human neutrophil elastase, and they could be a drug of cholice for the diseases which were known as pathogenesis related to elastase. We also suggest that the mechanism of action of these antibitics are different from the mechanism of antimicrobial effects like inhibition of both cell wall synthesis and protein synthesis.