Matrix metalloproteinase-9 (MMP-9) is a matrixin, a class of enzymes that belong to the zinc-metalloproteinases family involved in the degradation of the extracellular matrix. Proteins of the matrix metalloproteinase (MMP) family are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, angiogenesis, bone development, wound healing, cell migration, learning and memory, as well as in pathological processes, such as arthritis, intracerebral hemorrhage, and metastasis. MMP9 is synthesized as preproenzyme of 707 amino-acid residues, secreted as an inactive pro-MMP. Activation is achieved through an interacting protease cascade involving plasmin and stromelysin 1 (MMP-3). The enzyme degrades type IV and V collagens and other extracellular matrix proteins. MMP9 has been found to be associated with numerous pathological processes, including cancer, placental malaria, immunologic and cardiovascular diseases.