The 92-kD type IV collagenase is also known as 92-kD gelatinase, type V collagenase, gelatinase B, or matrix metalloproteinase-9(MMP9). The 72- and 92-kDa type IV collagenases are members of a group of secreted zinc metalloproteases.1 The matrix metalloproteinases(MMPs) are able to degrade the extracellular matrix and allow angiogenesis and tumor invasion. Gelatinase B, a matrix metalloproteinase that has proteolytic activity against connective tissue proteins, has been suggested to be important in the connective tissue remodeling processes associated with atherogenesis and plaque rupture. MMP-9 is predominantly expressed in neutrophils, macrophages, and mast cells, rather than in oncogene-positive neoplastic cells. The polymorphism of MMP-9 acts as a genetic factor for the development of smoking-induced pulmonary emphysema.