Triggered human neutrophils degraded denatured type I collagen (gelatin) by releasing and activating the latent metalloenzyme, gelatinase. The ability of the neutrophil to activate this enzyme was significantly, but not completely, inhibited by agents known to inhibit or scavenge chlorinated oxidants generated by the H2O2/myeloperoxidase/chloride system. A direct role for chlorinated oxidants in this process was confirmed by the ability of reagent HOCl to activate the latent enzyme in either the cell-free supernatant or in a highly purified state. Gelatinase activity was also expressed by triggered neutrophils isolated from patients with chronic granulomatous disease. The amount of gelatinolytic activity expressed by the patients' cells was similar to that released by normal neutrophils that were triggered in the presence of antioxidants. Thus, human neutrophils have the ability to activate gelatinase by either an HOCl-dependent process or an uncharacterized oxygen-independent process. The ability of the neutrophil to directly regulate this enzyme suggests an important role for the metalloproteinase in physiologic and pathophysiologic connective tissue metabolism.