Gliostatin is a polypeptide growth inhibitor of apparent M(r) = 100,000 with a homodimeric structure comprising two 50-kDa subunits, acting on astrocyte as well as astrocytoma cells (Asai, K., Hirano, T., Kaneko, S., Moriyama, A., Nakanishi, K., Isobe, I., Eksioglu, Y.Z., and Kato, T. (1992) J. Neurochem., 59, 307-317). The amino acid sequences of 13 tryptic peptides including the amino terminus were completely identical to those of platelet-derived endothelial cell growth factor (PD-ECGF) (Ishikawa, F., Miyazono, K., Hellman, U., Drexler, H., Wernstedt, C., Hagiwara, K., Usuki, K., Takaku, F., Risau, W., and Heldin, C.-H. (1989) Nature 338, 557-562). Gliostatin and PD-ECGF, purified from human placenta, shared growth inhibition on glial cells and growth promotion on endothelial cells, and exhibited similar values for half-maximal dose of glial growth inhibition (ID50 = 1.3 nM) and the half-maximal concentration of endothelial growth promotion (EC50 = 1.0 nM), suggesting that both factors evoke the biological actions through an identical receptor on each cell surface. We have further demonstrated evidence of a novel neurotrophic action of gliostatin/PD-ECGF toward embryonic rat cortical neurons in culture. The half-maximal concentration of gliostatin/PD-ECGF for neurotrophic action was 0.3 nM. All actions on glial, endothelial, and neuronal cells, were abolished by a monoclonal antibody against gliostatin. These data indicate that gliostatin/PD-ECGF may play important roles on development and regeneration of the central nervous system and may also involve the induction of angiogenesis for the formation of blood brain barrier.