Abstract: Brain-derived neurotrophic factor (BDNF) is one of the neurotrophins, a specific polypeptide growth factor, which plays a crucial role in the proliferation, differentiation, survival, and death of neurons and non-neuronal cells. It is not only essential to maintain the balance between death on one side and survival of neurons on the other, but also it mediates additional higher-order activities such as learning, memory, and behavior. It is initially synthesized as a precursor protein, proBDNF, that can be secreted as it is or it can be cleaved intracellularly by furin and proconvertases, or extracellularly by extracellular proteases such as matrix metalloprotease-9 and matrix metalloprotease-2, or plasmin to give mature BDNF.