Human neutrophil cathepsin-G, which has been known as one of the active enzymes causing inflammatory diseases, was purified by two steps procedure involving one size exclusion (Ultorogel AcA54) and one ion exchange (CM-Sephadex) chromatography. Purified HNCGs were cross-reacted with Anti-HNCathepsin-G antibodies which were radised in rabbits and purified by cathepsin-G labeled Sepharose 4B affinity chromatography. HNCGs were effectively inhibited by NSAIDs including phenylbutazone, sulindac, oxyphenbutazone, salicylic acid and salicyluric acid. IC₅₀s of these drugs for inhibition of Cathepsin G were 0.3-0.8 mM. Other NSAIDs including aspirin showed little or no inhibition effect on the activity of Cathepsin G. These results strongly indicated that NSAIDs which showed inhibition effect on the activity of HNCGs possibly be at least a part of mechanism of action which might be related to direct inhibition of cathepsin G at the tissue destruction sites beside of their known mechanism of action as an anticyclo-oxygenase in treatment of inflammatory diseases. Lipid soluble component of Korean Red Ginseng which was known as an anti-inflammatory agent inhibited HNCGs strongly, but no other fractions did inhibited HNCGs. Antibiotics including novobiosin and rifamycin showed some inhibition effect on HNCGs, i. e.., IC₅₀ of these drugs were 2.6 mM and 1.5 mM respectively, and other antibiotics including penicillin G showed no or negligible inhibition effect on the activity of HNCGs. However. tetracyclines inhibited HNCGs very effectively at the concentration of therapeutic range. The inhibition effect of the activity of HNCGs by tetracycline are not related to the N-dimethyl radical on the 4 position of the tetracycline molecule. Furthermore, N-dedimethylated tetracyclines may have beneficial effect for long term treatment of chronic inflammatory diseases without developing any drug resistance to microorganisms.