Neurotrophin-3 (NT-3) is a neurotrophic factor in the NGF family of neurotrophins. NT-3 has activity on certain neurons of the peripheral and central nervous systems, supporting survival and differentiation of existing and new neurons. Neurotrophins function primarily to regulate naturally occurring cell death of neurons during development. Two additional structurally homologous neurotrophic factors have been identified: brain-derived neurotrophic factor (BDNF) and neurotrophic 4 (NT-4), also designated NT-5.