p75 neurotrophin receptor, also named low affinity NGF receptor (NGF R), is a type I transmembrane protein that belongs to the tumor necrosis factor receptor family. The extracellular region contains four cysteine-rich domains and binds NGF, BDNF, NT-3 and NT-4 approximately equally with low affinity. The cytoplasmic region contains a subtype 2 death domain. NGF R expression has been shown to occur widely during development and in the adult. Expression has been detected in both neuronal and non-neuronal cells. NGF R was originally reported to function as a positive regulator of TrkA activity. NGF R has also been shown to signal by itself. Depending on its cellular environment, NGF R has now been shown to regulate cell migration, gene expression and to mediate apoptosis. Recombinant NGF R/Fc chimera binds NGF with high affinity and is a potent NGF antagonist. Naturally occurring truncated NGF R containing the extracellular domain and lacking the transmembrane or intracellular domain has been detected in vivo in urine, plasma and in amniotic fluid of humans and rats.