S100B is a member of the S100 family of proteins containing 2 EF-hand calcium-binding motifs and has been implicated in the regulation of cellular activities such as metabolism, motility and proliferation. In the nervous system, S100B is constitutively released by astrocytes into the extracellular space and at nanomolar concentrations, it can promote neurite outgrowth and protect neurons against oxidative stress. Within the central nervous system (CNS), S100B is thought to be a marker for astroglial activation, linking astrocyte dysfunction to schizophrenia. In addition to astrocytes, S100B is released from many cell types, such as, adipocytes, chondrocytes, cardiomyocytes and lymphocytes. Serum S100B represents a new bomarker for mood disorders.