The organs of the vestibular, auditory and lateral line systems rely on a common strategy for the stimulation of their primary receptors, the hair cells: stimuli induce shear between hair cell epithelia and accessory structures to which hair bundles, the hair cells' mechanosensitive organelles, are attached. The inner hair cells of the cochlea, whose hair bundles are not attached to the overlying tectorial membrane, are a notable exception. Because their hair bundles are not restrained, they undergo significant Brownian motion, a characteristic traditionally thought to blunt the sensitivity of hearing. Contrary to this view, the work reported here indicates that Brownian motion of the hair bundle serves to enhance the sensitivity of mechanoelectrical transduction.