Otoacoustic emissions (OAEs) are low-level acoustic sounds of cochlear origin that can be recorded from the external auditory canal under well-controlled conditions. They are a natural by-product of normal auditory physiology and may be divided into two general categories: spontaneous and evoked emissions. These emissions provide an objective, non-invasive measurement of cochlear function that is accurate, rapid, and simple to perform. The clinical utility of OAEs has been extensively described in both normally hearing subjects and subjects with sensori-neural hearing loss. The primary clinical applications of these emissions appear to be in neonatal screening and ototoxic monitoring. In this study, the effects of middle ear effusion on the production of evoked OAEs in children were assessed using preoperative tympanometric and otoacoustic emissions testing. The study subjects were children with a history of chronic otitis media who had otoscopic findings suggestive of middle ear effusion. An attempt was made to correlate the type of middle ear effusion found at surgery with the presence or absence of preoperative otoacoustic emissions. Statistical analysis indicated that the type of effusion in the middle ear does affect the presence or absence of emissions. These results tend to refute previous notions that OAEs are not measurable if the tympanogram is abnormal or fluid is present in the middle ear space. A review of the pertinent literature in included, along with a general description of the types of OAEs and their clinical significance.