Mice with targeted disruption of the TGF beta 2 gene display defects in epithelial-mesenchymal tissue interactions in several tissues including the developing cochlea. Specifically, the region of the spiral limbus and the overlying interdental cells, structures putatively involved in endolymphatic fluid homeostasis, display morphogenetic abnormalities. These findings prompted us to explore the pre-natal and post-natal expression of all three mammalian TGF beta genes in the developing mouse inner ear. TGF beta 2 mRNA expression was identified throughout the cochlear epithelium at all of the developmental stages examined. TGF beta 3 mRNA expression was identified in the mesenchymal tissues of the cochlea surrounding the otic epithelium. We found no evidence for compensation by the other two TGF beta isoforms in the cochleas of the TGF beta 2 mutants.