OBJECTIVES/HYPOTHESIS: The hair cells are the most vulnerable elements in the cochlea, and damage to them is the most common cause of sensorineural hearing loss. Understanding the intracellular events that lead to the death of hair cells is a key to developing protective strategies. The Fas death receptor-mediated apoptotic pathway is well studied and plays an important role in the elimination of damaged cells in a number of different cellular systems. We have studied the role of the Fas receptor in aminoglycoside-mediated toxicity in vitro. We employed the MRL/MpJ-Fas mouse, which does not express a functional Fas receptor. STUDY DESIGN: Response of Fas-deficient hair cells to gentamicin was compared with the response of normal hair cells in vitro. METHODS: Basal turn organ of Corti explants from p3-5 mice were maintained in tissue culture and treated with gentamicin for 72 hours. The explants were fixed and were stained with phalloidin, and counting was performed. RESULTS: There was no difference in hair cell loss between Fas mutant mice and control MRL/MpJ mice with a functional Fas receptor. CONCLUSION: The gentamicin-mediated hair cell death is not dependent on a functional Fas receptor.