Here we describe cloning of a TGF-beta related cytokine from a rat brain cDNA library. This novel cytokine, the vgr (vegetal related), is homologous to the vegetal (Vg1) gene of Xenopus (DL Weeks and DA Melton, Cell, 51:861-867, 1987). In rat brain mRNA a single 3.5 kb RNA could be detected by Northern blot analysis. Thus, this new cytokine is constitutively expressed in the central nervous system. A monoclonal antibody reactive with a synthetic peptide of vgr revealed a faint vgr-like immunoreactivity throughout the CNS, with more pronounced staining of hippocampal neurons, ependymal cells, cells of the choroid plexus, and hypophysis. Using the rat cDNA, two homologous human cytokine cDNAs encoding the human vgr and op-1 were cloned.