Neutrophil proteinases have the capacity to degrade almost every component of the extracellular matrix. In marked contrast to the wealth of available data about the structure and activity of these proteinases when they are free in solution, there has been relatively little information about the mechanisms by which neutrophils use and control their proteolytic enzymes in an extracellular milieu that is replete with proteinase inhibitors. However, recent data have provided insights into several mechanisms that permit these enzymes to evade inhibition: (1) compartmentalization; (2) localized inactivation of proteinase inhibitors; (3) tight binding of enzymes to substrates; and (4) binding of proteinases to the neutrophil's cell surface.