Transforming growth factor-beta (TGF-beta) is a homodimeric polypeptide which can act, often in cooperation with other growth factors, as a mitogenic factor for a variety of cells. TGF-beta can also exert growth inhibitory activity on many other cell lines. We have isolated cDNAs coding for the murine TGF-beta cDNA precursor. The deduced amino acid sequence localizes the 112-amino acid long TGF-beta monomer to the C terminus of the precursor. Two areas of the precursor exhibit a marked degree of homology to the human counterpart. One of these regions comprises the mature TGF-beta monomer, while the other corresponds to the NH2 terminus of the precursor and suggests an important biological function for this area. Northern hybridization results identify a major 2.5-kilobase TGF-beta mRNA and several minor TGF-beta mRNA species.