Nerve growth factor (NGF) plays an important role in regulating mammalian neuronal/embryonic development, angiogenesis, and other physiological processes and has recently been investigated as a potential treatment for the neurodegenerative disorder, Alzheimer disease. In this study, we provide evidence that human NGF may also function as a metalloproteinase inhibitor, based on studies of NGF from snake venom. Originally, our aim was to isolate snake venom metalloproteinases targeting platelet receptors and/or ligands relevant to hemostasis and thrombosis, using Ni(2+)-agarose as a purification step based on the conserved metal ion-coordination motif in venom metalloproteinases. However, subsequent analysis of cobra (Naja kaouthia) venom led to the unexpected discovery that cobra venom NGF bound to Ni(2+)-agarose, eluting at approximately 15 mm imidazole, enabling a one-step purification. The identity of the purified protein was confirmed by mass spectrometry and N-terminal sequence analysis. Partial co-purification of NGF within metalloproteinase-enriched venom fractions led us to test whether NGF affected metalloproteinase activity. Venom NGF potently inhibited metalloproteinases isolated from the same or different venom and specifically bound to purified Nk metalloproteinase immobilized on agarose beads. Human NGF also interacted with human metalloproteinases because it blocked metalloproteinase-mediated shedding of the platelet collagen receptor, glycoprotein (GP)VI, and associated with recombinant ADAM10 by surface plasmon resonance. Together, these results suggest that NGF can function as a metalloproteinase inhibitor.