Azurocidin (AZU1), also known as heparin-binding protein (HBP) or cationic antimicrobial protein 37 (CAP37), is an azurophil granule antibiotic protein, with monocyte chemotactic and antibacterial activity. The Azurophil granules, specialized lysosomes of the neutrophil, contain at least 10 proteins implicated in the killing of microorganisms. Azurocidin is a member of the serine protease family that includes Cathepsin G, neutrophil elastase (NE), and proteinase 3 (PR3), however, Azurocidin is not a serine proteinase since the active site serine and histidine residues are replaced. Neutrophils arriving first at sites of inflammation release Azurocidin, which acts in a paracrine fashion on endothelial cells causing the development of intercellular gaps and allowing leukocyte extravasation. It thus be regarded as a reasonable therapeutic target for a variety of inflammatory disease conditions.