Otoacoustic emissions" OAEs# are low intensity sounds gen! erated within the normal cochlea and emitted from the exter! nal auditory meatus\either spontaneously or in response to acoustic stimulation [The _rst measurement of OAEs was reported in 0867 by David Kemp [0 They are thought to re~ ect active biological mechanisms within the cochlea responsible for the exquisite sensitivity\sharp frequency selectivity and wide dynamic range of the normal auditory system [Moreover\this active cochlear process is presently thought to be based in the outer hair cells [Outer hair cell movement" mobility# generates mechanical energy within the cochlea that is believed to propagate outward through the middle ear system to the external auditory meatus [Sounds produced in this manner are termed OAEs and can be measured using a sensitive micro! phone [When outer hair cells are structurally damaged or nonfunctional\OAEs cannot be evoked by acoustic stimuli [1 Because the measurement of OAEs is simple\fast\objective\reproducible and noninvasive\and because reduced OAE amplitudes are associated with certain types of hearing impair! ment\over the past 19 years\OAEs have been used in clinical settings to detect cochlear lesions resulting from factors such as ototoxic drug administration\noise overexposure\Men! ie¡ re| s disorder\sudden idiopathic hearing impairment\pre! sbyacusis\and hereditary hearing disorders [In addition\OAEs have also been used as an indicator of the presence of hearing impairment in neonates [1–3 However\OAEs generated within the cochlea must pass through the middle ear to their measurement site in the exter! nal auditory meatus\and they are reduced when sound con! duction through the middle ear system is compromised [There! fore\great care must be taken to ensure normal middle ear status if the OAEs are to be utilized as an index of cochlear function [