Both the hearing and vestibular organs of vertebrates contain cells responsive to miniscule mechanical disturbances. The common element is the hair cell, a sensory cell with a specialized mechanoreceptor at its apical end and with a basolateral membrane designed to shape the receptor potential and control synaptic interaction at its basal pole. The way in which hair cells are assem­ bled varies from species to species. This short review, with the main emphasis on hearing structures (see further 37, 38,49, 50), will highlight some of the differences found between hair cells and describe the features that makes them effective transducers-their ability to convert mechanical stimuli into neural codes.