Several connexin genes (GJB1, GJB2, GJB3, GJB6 and GJA1) have been found mutated in patients with non-syndromic and/or syndromic deafness indicating an important role of these proteins in the auditory system. In order to better understand the function of the connexins in the inner ear we have analyzed the gene expression profiles of two connexin genes, Gjb1 (connexin 32) and Gjb3 (connexin 31), by in situ hybridization during the mouse cochlea organogenesis, from early otocyst up to the mature organ in adult. In the developing otocyst epithelium, some restricted domains expressed Gjb3 and Gjb1 whilst high levels of both transcripts were present in the surrounding mesenchymal tissue. As development proceeds, expression of these two genes was found in various subtypes of fibrocytes, either within the spiral limbus or along the spiral ligament, as well as in the basilar membrane cells, in the Reissner's membrane cells, and in subsets of the cellular elements of the cochlear ganglion. Gjb3 and Gjb1 expression was spatiotemporally modulated within the sensory hair cells and the various supporting cells that compose the developing organ of Corti. A transitory expression of Gjb1 was found in the basal and intermediate cells of the stria vascularis. In the adult cochlea Gjb1 transcripts disappeared while Gjb3 expression remained present in fibrocytes with specific expression patterns.