Murine transforming growth factor-beta 3 (TGF beta 3) cDNAs were isolated from a TGF beta 2-induced AKR-2B cDNA library. The composite cDNA sequence is 2894 nucleotides long, including 610-nucleotide and 1054-nucleotide 5' and 3' untranslated sequences, respectively. The murine TGF beta 3-coding region is 1230 nucleotides in length and encodes a precursor protein of 410 amino acids, with a 96% peptide sequence identity with the human TGF beta 3 precursor. Examination of TGF beta 1 and TGF beta 3 mRNA levels in adult murine tissues showed that TGF beta 1 mRNA expression is predominant in spleen, lung, and placenta. In contrast, TGF beta 3 RNA was present in substantial amounts in brain, heart, adipose tissue, and testis. TGF beta 3 mRNA is also observed in adult mouse lung and placenta. Both TGF beta 1 and TGF beta 3 RNAs were present in all stages of mouse fetal development studied from 10.5-17.5 days postcoitum, with higher levels observed in the latter stages. The differential expression of these TGF beta genes suggests that the various TGF beta species may have distinct physiological roles in vivo.