Proteolytic enzymes play a key role in a variety of physiological processes in which the degradation of macromolecules is essential: angiogenesis, embryogenesis, bone and tissue remodelling, blood hemostasis and cell migration. The action of these enzymes is also crucial in the development of many pathological conditions such as wound healing, neoplasia, inflammation and arthritic disorders. The activity of proteases is negatively affected by specific protease-inhibitors. Various growth factors and other cytokines modulate the synthesis and secretion of both proteases and protease-inhibitors. The study of this regulation results in a better insight into (patho)physiology at the molecular level and promises to result in alternative treatment strategies.