AbstractThe transforming growth factor beta (TGF-β) family of growth modulators play critical roles in tissue development and maintenance. Recent data suggest that individual TGF-βisoforms (TGF-β1, -β2 and -β3) have overlapping yet distinct biological actions and target cell specificities, both in developing and adult tissues. The TGF-β3 isoform was purified to homogeneity from both natural and recombinant sources and characterized by laser desorption mass spectrometry, by protein sequencing, by amino acid analysis and by biological activity. TGF-β3 was the major TGF-βisoform in umbilical cord (230 ng/g), and was physically and biologically indistinguishable from recombinant TGF-β3 and from the tumor growth inhibitory (TGI) protein found in umbilical cord. Immunohistochemistry using antipeptide TGF-β3 specific antibody showed TGF-β3 localization in perivascular smooth muscle.