The focus of this research is age-related hearing loss (presbyacusis). Currently, nearly 28 million Americans have impaired hearing, and approximately 75% of these persons are over the age of 55. The prevalence of presbyacusis will increase substantially by the year 2020. To meet the challenges of this most prevalent handicapping condition, new information, diagnostic methods, rehabilitation procedures, and cost-effective access to new technologies will be of great importance. Prevention of presbyacusis and/or a reduction in its prevalence are even greater challenges. The overall objective of our research program is to improve diagnostic, rehabilitive, and preventive measures. Towards this objective, four research projects are proposed. Project 1 is a study of the basic psychophysical and electrophysiological properties of the aging auditory system of human subjects. Project 2 addresses basic questions related to the understanding of speech in realistic listening environments by young and older human subjects with normal and impaired hearing. Project 3 focuses on morphologic and molecular changes in the aging cochlea of gerbil and human subjects. Project 4 investigates neurotrophins and their role in regulating the survival of adult auditory and vestibular neurons using both gerbil and human tissue. In addition, three cores provide administrative, technical,, and scientific support including the procurement and maintenance of laboratory animals, recruitment of human subjects, and retrieval of human tissues. The proposed program of research of presbyacusis in the long term will influence health care of the presbyacusic patient, will affect care of hearing impaired persons in general, and will have significant impact on theoretical issues in the science of audition.