OBJECTIVE:Recent studies have identified the capacity of transforming growth factor‐α (TGF‐α) to stimulate mammalian labyrinthine hair cell regeneration after acute ototoxic damage. Augmenting hair cell regeneration with such growth factors may have a role in potentiation of recovery of cochlear function after hair cell injury. Transtympanic application of aqueous solutions to the round window membrane (RWM) has proved successful as a drug delivery route. The purpose of this study was to test the permeability of the mammalian RWM to TGF‐α in an inexpensive and reliable in vitro model.METHODS:Guinea pig RWM niches were harvested and transferred to a 2‐chamber apparatus, and TGF‐α was applied to the middle‐ear side of the chamber. ELISAs of TGF‐α were measured at intervals during a 96‐hour period.RESULTS:Aliquots taken during a 96‐hour interval demonstrated passage of TGF‐α in concentrations sufficient to stimulate hair cell regrowth.CONCLUSIONS:The apparatus allows study of RWM permeability to other substances and provides a basic model for study of RWM physiology. TGF‐α is able to pass through a mammalian RWM.