A targeting vector was generated using recombineering methods to modify a BAC containing the Slc26a5 (prestin) locus. An IRES-cre/ERT2-frt-neo-frt cassette was inserted after the stop codon in exon 20. The vector was electroporated into TL-1 ES cells to produce knockin mice. When crossed to EGFP reporter mice, cre activity was observed in outer hair cells in the cochlea at P2 with tamoxifen treatment at P0. No reporter signal could be detected in vestibular organs, testis or brain (tissues that express Slc26a5 at low levels.)