The overall goal of this research is to explore the limits of distortion product otoacoustic emissions (DPOAE) measurements and to determine the relation between DPOAE parameters and cochlear damage in humans. This general goal will be addressed in a series of experiments in which the primary questions are (1) how well can the presence and magnitude of hearing loss be predicted from DPOAE measurements?; (2) does cochlear damage in one frequency region influence DPOAE measurements from other regions?; (3) is less DPOAE energy measured in the low frequencies compared to high frequencies and what are the factors affecting this outcome:; (4) do measures of DPOAE latencies in normal ears depend on intensity and do they shorten in impaired ears, reflecting the loss in nonlinear behavior"; (5) is the shape and/or location of the DPOAE filter affected by hearing loss. Statistical principles, many of which have been applied to clinical decisions in other medical disciplines (i.e., radiology), will be used here to evaluate these data. In answering the above questions, efforts will be devoted to large scale studies in patients with hearing loss, to projects designed to provide information that will help to determine the optimum conditions for test performance, and to projects that should provide greater insight into aspects of cochlear processing in humans. These studies eventually may lead to the development of techniques that result in a greater understanding of the consequences of cochlear hearing loss in humans, which occurs in approximately 22 million U.S. citizens.