Transforming growth factor beta (TGFß) genes are linked to a variety of developmental processes and are the subject of in vivo and in vitro transgene research studies. We are evaluating TGFß-2 effects on mouse inner ear development, with emphasis on the cochlear duct (CD), by comparing plastic sections of intact inner ears from developmental day (D) 16.5,18.5 and 19.5 littermates with wildtype (+/+), heterozygous (+/−) and mutant (−/−) TGFß-2 genotypes as determined by polymerase chain reaction analysis of tail digests. Auditory and vestibular organs of all D16.5 mice appear similar: membranous labyrinth epithelium varies from simple cuboidal/low columnar to pseudostratified/stratified columnar. Surrounding mesenchyme varies in cell density regionally, the most cellular mesenchyme underlies areas of sensory epithelium. Sparse mesenchymal cell distribution in the vestibule and basal CD indicates sites of perilymph channel formation. The spiral and vestibular ganglia and their unmyelinated fibers are prominent. Otoconia and hair cells are present in the utricle (U) and saccule (S) maculae; hair cells are less easily identifiable in the CD.